Interesting Objects listed by size
Here is a list of 313 interesting extended objects. They are listed
by size in order to emphasize the idea that when imaging extended objects
is is necessary to try to get a significant sized image on the film or
chip so as to make good use of the resolving power of the film or imager.
The only way to essentially "fill the chip" with the image is to use the
proper focal length telescope. The proper focal length can be obtained
by choosing the telescope focal length and augmenting it with suitable
focal reducers. The full list is interrupted in to groups
with headings which give some common optical choices that "fill the chip."
(At the very end of the list is a short discussion of what I have used
as a criterion for "filling the chip.")
The first set of objects is very small, up to about 1 by 1.5 arc minutes. With a 3000 mm telescope (12" f10) this yields a largest image size at the chip of only 0.9 mm (90 pixels). This is not a very high resolution situation but probably all that can be expected. The atmospheric resolution, under good seeing conditions, is only about 1 arc second which is about one pixel with this focal length. There are 28 objects in this category including 4 M objects. While it is difficult to get great detail in these objects with a telescope of 3000 mm focal length, It would probably be wise to use a 2X focal extender to get a bigger image on the chip. These objects are tiny and quite faint. It seems amazing that Messier was able to see the four on this list. Note that all of the planets are in this range or much smaller than the smallest of these objects. Jupiter, the largest is about 40 arc seconds (0.7 arc minutes), Saturn about 20 to 30, Venus 10 to 60 and the rest very small. To image such small objects, projection imaging or a 3X to 5X focal extender is usually used to get a larger image. With very dim objects, such as those listed here, there is not enough light to use projection imaging. There is no substitute for a large, long focal length telescope for imaging these tiny, dim objects.
NUMBER Messier RA
DEC SIZE
MAG TYPE
UGC 7772 M 040 12 22.4
58 05
9.0 Double Star
NGC 1535
04 14.4 -12 44 0.3x0.3
9.0 Planetary Nebula
NGC 6210
16 44.6 23 47 0.3x0.3
9.7 Planetary Nebula
NGC 7027
21 07.0 42 14 0.3x0.2
9.0 Planetary Nebula
NGC 6826
19 44.7 50 31 0.4x0.4
8.8 Planetary Nebula
NGC 7009
21 04.1 -11 22 0.4x0.4
8.0 Planetary Nebula
NGC 6543
17 58.8 66 38 0.4x0.3
8.6 Planetary Nebula
NGC 7662
23 25.9 42 33 0.5x0.5
8.5 Planetary Nebula
NGC 4782
12 54.6 -12 35 0.5x0.5
12.9 Elliptical Galaxy 0
NGC 4783
12 54.6 -12 34 0.5x0.5
12.9 Elliptical Galaxy 0
NGC 2392
07 29.2 20 55 0.7x0.7
8.3 Planetary Nebula
NGC 3242
10 24.8 -18 38 0.7x0.7
8.9 Planetary Nebula
NGC 4476
12 30.0 12 20 0.7x0.4
13.3 Elliptical Galaxy 4
NGC 0040
00 12.9 72 32 1.0x0.7
10.5 Planetary Nebula
NGC 4889
13 00.1 27 59 1.0x0.6
13.2 Elliptical Galaxy 4
NGC 6729
19 01.8 -36 58 1.0x1.0
? Nebula
NGC 6994 M 073 20 58.9
-12 39 1.0x1.0 10.0
Open Cluster
NGC 7006
21 01.4 16 12 1.0x1.0
11.5 Globular Cluster
NGC 0604
01 34.5 30 46 1.0x1.0
? Nebula
NGC 2346
07 09.3 00 49 1.0x0.9
10.0 Planetary Nebula
NGC 4413
12 26.5 12 36 1.1x0.7
13.2 Barred Spiral a
NGC 2438
07 41.9 -14 43 1.1x1.1
11.0 Planetary Nebula
NGC 0278
00 52.0 47 34 1.2x1.2
11.6 Spiral Galaxy c
NGC 6720 M 057 18 53.6
33 02 1.3x1.0 9.0
Planetary Nebula
NGC 5367
13 57.7 -39 59 1.3x1.0
10.0 Nebula
NGC 4435
12 27.7 13 04 1.4x0.9
11.8 Elliptical Galaxy 4
NGC 0650-1 M 076 01 41.9 51
34 1.5x0.7 10.0
Planetary Nebula
NGC 4459
12 29.0 13 58 1.5x1.0
11.7 Spiral Galaxy 0
The next batch of objects goes up to about 3 arc minutes. Even these objects create quite a small image with the 3000 mm telescope. But these images are up to 200 pixels in size. This is a good sized image on an ST-7 size chip which is about 500 by 750 pixels. Pictures taken with this resolution are nice to look at but but still do not use up the chip area available and are nowhere near photographic quality. There are 39 objects in this group and only 5 are M objects.
NGC 4479
12 30.3 13 35 1.5x1.5
12.5 Spiral Galaxy b
NGC 4105
12 06.7 -29 47 1.5x1.5
12.0 Elliptical Galaxy 3
NGC 4478
12 30.3 12 19 1.0x1.8
12.4 Elliptical Galaxy 1
NGC 2782
09 14.1 40 07 1.8x1.6
12.4 Spiral Galaxy b
NGC 4106
12 06.8 -29 48 1.0x1.8
12.0 Elliptical Galaxy 2
NGC 2732
09 13.4 79 11 1.8x0.8
11.9 Spiral Galaxy c
NGC 4387
12 25.7 12 49 1.9x1.1
12.0 Elliptical Galaxy 5
NGC 4458
12 29.0 13 15 1.9x1.8
12.0 Elliptical Galaxy 0
NGC 2261
06 39.1 08 43 2.0x2.0
10.0 Nebula
NGC 2419
07 38.2 38 53 2.0x2.0
11.0 Globular Cluster
NGC 4374 M 084 12 25.1
12 53 2.0x1.8 10.5
Elliptical Galaxy 1
NGC 4402
12 26.1 13 07 2.0x0.8
13.0 Spiral Galaxy b
NGC 4425
12 27.2 12 44 2.0x0.5
12.9 Spiral Galaxy 0
NGC 4461
12 29.1 13 11 2.0x1.0
12.2 Spiral Galaxy 0
NGC 4473
12 29.8 13 25 2.0x1.0
11.3 Elliptical Galaxy 4
NGC 4621 M 059 12 42.0
11 39 2.0x1.5 11.0
Elliptical Galaxy 3
NGC 6302
17 13.9 -37 07 2.0x1.0
? Nebula
NGC 5195
13 30.0 47 16 2.0x1.5
11.0 Peculiar Galaxy
NGC 1999
05 36.5 -06 43 2.0x2.0
9.0 Nebula
NGC 6638
18 31.0 -25 30 2.0x2.0
9.5 Globular Cluster
NGC 6642
18 31.8 -23 29 2.0x2.0
8.0 Globular Cluster
NGC 6652
18 35.8 -33 00 2.0x2.0
8.5 Globular Cluster
NGC 6934
20 34.1 07 24 2.0x2.0
9.0 Globular Cluster
NGC 6569
18 13.7 -31 49 2.0x2.0
10.0 Globular Cluster
NGC 7335
22 37.3 34 27 1.7x0.8
14.7 Galaxy so
NGC 3379 M 105 10 47.8
12 35 2.1x2.0 10.6
Elliptical Galaxy 1
NGC 3389
10 48.4 12 32 2.2x1.0
12.2 Spiral Galaxy c
NGC 4567
12 36.5 11 15 2.4x1.6
12.0 Elliptical Galaxy s1
NGC 5908
15 16.7 55 25 2.4x0.4
13.0 Spiral Galaxy b
NGC 1068 M 077 02 42.7
-00 01 2.5x1.7 10.0
Spiral Galaxy b
NGC 3587 M 097 11 14.9
55 02 2.5x2.5 11.0
Planetary Nebula
NGC 4038
12 01.9 -18 52 2.5x2.5
11.0 Peculiar
NGC 4039
12 01.9 -18 53 2.5x2.0
12.0 Peculiar
NGC 4697
12 48.6 -05 48 2.5x1.3
10.5 Elliptical Galaxy 3
NGC 2207
06 16.4 -21 22 2.5x1.5
12.3 Spiral Galaxy c
NGC 3077
10 03.4 68 44 2.6x1.9
11.0 Elliptical Galaxy 2
NGC 1275
03 19.8 41 31 2.6x1.0
11.6 Syfert Galaxy
NGC 2748
09 13.7 76 29 2.8x1.1
11.7 Spiral Galaxy c
NGC 3513
11 03.8 -23 15 2.9x2.3
11.5 Spiral Galaxy c
The next group of objects is up to 3.6 arc minutes in size. This corresponds to an image of almost 400 pixels size. These objects really fill the ST-7 chip using the full focal length of the 12" f10. Even the 10" f10 gives a reasonable image size and might be considered for imaging these objects. There are 21 objects in the group but only 8 of them M objects.
NGC 4382 M 085 12 25.3
18 11 3.0X2.0 10.5
Spiral Galaxy 0
NGC 4406 M 086 12 26.2
12 56 3.0X2.8 10.5
Elliptical Galaxy 3
NGC 4486 M 087 12 30.8
12 23 3.0x3.0 8.6
Elliptical Galaxy 1
NGC 4649 M 060 12 43.6
11 33 3.0x2.5 10.0
Elliptical Galaxy 1
NGC 6171 M 107 16 32.5
-13 03 3.0x3.0 8.1
Globular Cluster
NGC 6864 M 075 20 06.1
-21 55 3.0x3.0 8.0
Globular Cluster
NGC 6981 M 072 20 53.5
-12 33 3.0x3.0 8.6
Globular Cluster
NGC 3626
11 20.1 18 21 3.0x2.0
10.9 Spiral Galaxy b
NGC 5824
15 04.0 -33 05 3.0x3.0
9.5 Globular Cluster
NGC 6441
17 50.2 -37 03 3.0x3.0
8.0 Globular Cluster
NGC 6624
18 23.7 -30 22 3.0x3.0
8.5 Open Cluster
NGC 6712
18 53.0 -08 43 3.0x3.0
9.0 Globular Cluster
NGC 7339
22 37.8 23 47 3.0x0.9
12.1 Spiral Galaxy c
NGC 5248
13 37.6 08 53 3.2x1.4
11.0 Spiral Galaxy c
NGC 4298
12 21.5 14 36 3.2x1.9
11.4 Spiral Galaxy c
NGC 4710
12 49.6 15 10 3.4x0.5
12.0 Spiral Galaxy 0
NGC 0185
00 38.5 48 21 3.5x2.8
11.8 Elliptical galaxy 1
NGC 7479
23 04.9 12 19 3.2x3.5
11.8 Barred Galaxy b
NGC 6229
16 47.0 47 32 3.5x3.5
8.9 Globular Cluster
NGC 0221 M 032 00 42.7
40 52 3.6x3.1 9.5
Elliptical galaxy 2
NGC 5694
14 39.6 -26 32 3.6x3.6
10.2 Globular Cluster
The next group of objects goes up in size to 5.5 arc minutes. Now the largest of these images is a full 480 pixels in size and will fill the ST-7 chip almost completely. These are the largest size objects that can be imaged and still fit fully on the ST-7 chip when using the 12" f10. Even then a focal reducer might be considered to trade image size for telescope speed and thus shorter exposure times. An ST-8 moght be considered for these objects as well. The objects also give a nice sized image with the 10" f10. Even the 10" f6.3 will give up to a 200 pixel image. There are 37 objects in this group with 13 of them being M objects.
NGC 0246
00 47.1 -11 53 4.0x2.5
8.5 Planetary Nebula
NGC 3115
10 05.3 -07 43 4.0x1.0
10.0 Elliptical Galaxy 7
NGC 3351 M 095 10 43.9
11 42 4.0x3.0 11.0
Barred Spiral c
NGC 3384
10 48.3 12 38 4.0x2.0
11.0 Elliptical Galaxy 7
NGC 4438
12 27.8 13 00 4.0x1.5
11.0 Spiral Galaxy a
NGC 4472 M 049 12 29.8
07 59 4.0x3.4 10.1
Elliptical Galaxy 3
NGC 4477
12 30.0 13 38 4.0x3.5
10.4 Barred Spiral a
NGC 4579 M 058 12 37.6
11 48 4.0x3.5 10.5
Spiral Galaxy b
NGC 6333 M 009 17 19.1
-18 31 4.0x4.0 8.0
Globular Cluster
NGC 6637 M 069 18 31.4
-32 21 4.0x4.0 7.5
Globular Cluster
NGC 6681 M 070 18 43.3
-32 18 4.0x4.0 8.0
Globular Cluster
NGC 0559
01 29.5 63 18 4.0x4.0
9.5 Open Cluster
NGC 7235
22 12.5 57 15 4.0x4.0
9.0 Open Cluster
NGC 6603
18 18.4 -18 26 4.0x4.0
11.4 Open Cluster
NGC 4449
12 28.2 44 05 4.2x3.0
10.5 Irregular Galaxy
NGC 7332
22 37.4 23 47 4.2x1.3
11.0 Spiral Galaxy c
NGC 4111
12 07.1 43 04 4.4x0.9
10.7 Spiral Galaxy c
NGC 4254 M 099 12 18.8
14 25 4.5X4.0 10.4
Spiral Galaxy c
NGC 2775
09 10.3 07 02 4.5x3.0
10.3 Spiral Galaxy b
NGC 4302
12 21.7 14 36 4.5x0.5
12.9 Spiral Galaxy c
NGC 5005
13 10.8 37 03 4.7x1.6
10.8 Spiral Galaxy b
IC 2233
08 14.2 45 44 4.7x0.6
13.0 Spiral Galaxy c
NGC 1952 M 001 05 34.5
22 01 5.0x3.0 9.0
Nebula
NGC 4388
12 25.8 12 39 5.0x1.0
12.0 Barred Spiral b
NGC 4736 M 094 12 51.0
41 07 5.0x3.5 8.9
Spiral Galaxy b
NGC 6779 M 056 19 16.5
30 10 5.0x5.0 8.0
Globular Cluster
NGC 2129
06 01.1 23 18 5.0x5.0
7.0 Open Cluster
NGC 5466
14 05.4 28 32 5.0x5.0
9.0 Globular Cluster
NGC 5986
15 46.1 -37 46 5.0x5.0
8.0 Globular Cluster
NGC 6520
18 03.5 -27 54 5.0x5.0
9.0 Open Cluster
NGC 0779
01 59.7 -05 57 3.0x5.0
11.8 Spiral Galaxy b
NGC 4490
12 30.7 41 38 5.0x2.0
10.1 Spiral Galaxy c
NGC 4321 M 100 12 22.9
15 49 5.2x5.0 10.4
Spiral Galaxy c
NGC 5866/79 M 102? 15 06.5 55 45
5.2x2.3 10.0 Elliptical Galaxy
NGC 4548 M 091 12 35.5
43 09 5.4x4.4 10.2
Spiral Galaxy c
NGC 7814
00 03.3 16 09 1.5x5.5
11 Spiral Galaxy b
NGC 3511
11 03.4 -23 05 5.5x1.0
11.0 Spiral Galaxy c
The next group of objects goes up to 9.9 arc minutes in size. This is 870 pixels with the 12" f10. Clearly these objects give images that no longer fit on the ST-7 chip. At this point it is good to consider the ST-8 which has a chip of twice the size and four times the area. The 12" f10 must be used with a focal reduce of at least 0.63 strength on the ST-7. The 10" f10 now gives the excellent sized images up to 580 pixels. But the 10" f6.3 looks like a good choice as well, giving images up to about 360 pixels. This is a very large group of 67 objects with no less than 35 M objects. With the 10" f 6.3 scope and the ST-8 a very comfortable match is had.
NGC 4303 M 061 12 22.0
04 28 5.7x5.5 10.2
Spiral Galaxy c
NGC 4501 M 088 12 32.0
14 25 5.7x2.5 10.5
Spiral Galaxy b
NGC 6934
20 34.2 07 24 5.9x5.9
8.9 Globular Cluster
NGC 5377
13 56.3 47 12 3.0x6.0
12.0 Spiral Nebula a
NGC 2362
07 18.7 -24 57 6.0x6.0
4.0 Open Cluster
NGC 3368 M 096 10 46.8
11 49 6.0x4.0 10.2
Spiral Galaxy b
NGC 6266 M 062 17 01.3
-30 07 6.0x6.0 6.5
Globular Cluster
NGC 6273 M 019 17 02.6
-26 15 6.0x6.0 7.0
Globular Cluster
NGC 6402 M 014 17 37.6
-03
15 6.0x6.0 9.0
Globular Cluster
NGC 6626 M 028 18 24.6
-24 52 6.0x6.0 8.0
Globular Cluster
NGC 6715 M 054 18 55.2
-30 28 6.0x6.0 9.0
Globular Cluster
NGC 6838 M 071 19 53.7
18 47 6.0x6.0 9.0
Globular Cluster
NGC 7099 M 030 21 40.3
-23 11 6.0x6.0 8.0
Globular Cluster
NGC 7793
23 57.9 -32 34 6.0x4.0
9.7 Spiral Galaxy
NGC 1300
03 19.8 -19 24 6.0x3.2
11.3 Barred Spiral b
NGC 6819
19 41.3 40 13 6.0x6.0
10.0 Open Cluster
NGC 3432
10 52.5 36 37 6.2x1.7
10.6 Spiral Galaxy c
NGC 3992 M 109 11 57.6
53 22 6.4x3.5 10.9
Barred Spiral b
NGC 0147
00 33.1 48 31 6.5x3.8
12.1 Elliptical galaxy 4
NGC 1982 M 043 05 35.6
05 16 7.0x5.0 8.0
Nebula
NGC 4569 M 090 12 36.8
13 09 7.0x2.5 9.0
Spiral Galaxy b
NGC 4594 M 104 12 39.9
-11 37 7.0x1.5 8.2
Spiral Galaxy a
NGC 6093 M 080 16 17.1
-22 59 7.0x7.0 8.0
Globular Cluster
NGC 6613 M 018 18 19.9
-17 08 7.0x7.0 8.0
Open Cluster
NGC 6913 M 029 20 24.0
38 31 7.0x7.0 7.0
Open Cluster
NGC 7089 M 002 21 33.5
-00 50 7.0x7.0 6.0
Globular Cluster
NGC 6885
20 12.0 26 29 7.0x7.0
5.7 Open Cluster
NGC 2506
08 00.2 -10 47 7.0x7.0
7.6 Open Cluster
NGC 6723
18 59.6 -36 38 7.0x7.0
6.0 Globular Cluster
NGC 6997
20 56.5 44 39 7.0x7.0
10.0 Open Cluster
NGC 1904 M 079 05 24.3
-24 31 7.5x7.5 8.4
Globular Cluster
NGC 4826 M 064 12 56.8
21 41 7.5x3.5 8.6
Spiral Galaxy a
NGC 1055
02 41.8 42 21 7.6x3.0
10.6 Spiral Galaxy c
NGC 3079
10 02.0 55 41 7.6X1.7
10.6 Spiral Galaxy c
NGC 3556 M 108 11 11.6
55 41 7.8x1.4 10.8
Spiral Galaxy c
NGC 3623 M 065 11 18.9
13 07 7.8x1.6 10.3
Spiral Galaxy c
NGC 5746
14 44.9 01 57 7.9x1.7
10.6 Spiral Galaxy c
NGC 0205 M 110 00 40.3
41 41 8.0x3.0 10.8
Elliptical galaxy 6
NGC 0581 M 103 01 33.2
60 42 8.0x8.0 8.0
Open Cluster
NGC 2068 M 078 05 46.8
00 03 8.0x6.0 8.0
Nebula
NGC 3034 M 082 09 56.1
69 42 8.0x3.0 9.2
Irregular Galaxy
NGC 3627 M 066 11 20.2
13 01 8.0x2.5 9.7
Spiral Galaxy b
NGC 6254 M 010 16 57.1
-04 07 8.0x8.0 7.0
Globular Cluster
NGC 6341 M 092 17 17.1
43 09 8.0x8.0 6.5
Globular Cluster
NGC 6853 M 027 19 59.6
22 43 8.0x6.0 8.0
Planetary Nebula
NGC 6946
20 35.0 60 08 8.0x8.0
11.1 Spiral Galaxy c
NGC 1365
03 33.7 -36 08 8.0x3.5
11.2 Spiral Galaxy b
NGC 1502
04 07.4 62 19 8.0x8.0
7.0 Open Cluster
NGC 2627
08 37.3 -29 56 8.0x8.0
9.0 Open Cluster
NGC 6866
20 03.7 44 10 8.0x8.0
8.0 Open Cluster
NGC 6939
20 31.4 60 38 8.0x8.0
10.0 Open Cluster
NGC 4192 M 098 12 13.8
14 54 8.2x2.0 11.0
Spiral Galaxy b
NGC 4216
12 15.9 13 09 8.3x2.2
10.0 Spiral Galaxy c
NGC 2683
08 52.7 33 25 8.4x2.4
9.7 Spiral Galaxy c
NGC 5897
15 17.4 02 05 8.5x8.5
9.0 Globular Cluster
NGC 0628 M 074 01 36.7
15 47 9.0x9.0 9.0
Spiral Galaxy c
NGC 1097
02 46.4 -30 16 9.0x5.5
10.6 Barred Spiral b
NGC 4590 M 068 12 39.5
-26 45 9.0x9.0 8.0
Globular Cluster
NGC 5055 M 063 13 15.7
42 01 9.0x4.0 9.8
Spiral Galaxy b
NGC 6694 M 026 18 45.2
-09 24 9.0x9.0 9.5
Open Cluster
NGC 1857
05 20.1 39 21 9.0x9.0
7.0 Open Cluster
NGC 6649
18 33.5 -10 24 9.0x9.0
9.0 Open Cluster
NGC 2818
09 16.0 -36 37 9.0x9.0
11.0 Open Cluster
NGC 7788
23 56.7 61 24 9.0x9.0
9.4 Open Cluster
NGC 4762
12 52.9 11 14 9.1x2.2
10.3 Spiral Galaxy c
NGC 1560
04 32.8 71 53 9.2x1.7
11.5 Spiral Galaxy c
NGC 4517
12 32.8 00 07 9.9x1.4
10.4 Spiral Galaxy c
The next group has sizes up to 14 arc minutes. With the 10" f10 this is 820 pixels and thus requires a focal reducer on the 10" or a 10" f6.3 if the ST-7 is used. The image size is about 470 pixels which still fits on the ST-7 chip. Here is where the ST-8 chip size is a clear advantage. Objects at the end of this part of the list can now be imaged nicely on the ST-8 chip or with 35 mm format. The full focal length of the 12" f10 giving a generous image of 12 mm size. There are 36 objects, 11 of them being M objects.
NGC 0457
01 19.0 58 20 10x10
7.0 Open Cluster
NGC 2023
05 41.7 -02 13 10x10
? Nebula
NGC 2323 M 050 07 02.9
-08 20 10x10 6.0
Open Cluster
NGC 2360
07 17.7 -15 38 10x10
9.0 Open Cluster
NGC 4559
12 36.0 27 57 10x3
10.5 Spiral Galaxy c
NGC 5024 M 053 13 12.9
18 10 10x10 8.0
Globular Cluster
NGC 5194/5 M 051 13 29.9 47
12 10x5 8.1
Spiral Galaxy c
NGC 5236 M 083 13 37.1
-29 52 10x8
8.0 Spiral Galaxy c
NGC 6218 M 012 16 47.2
-01 57 10x10 8.0
Globular Cluster
NGC 6531 M 021 18 04.8
-22 30 10x10 7.0
Open Cluster
NGC 7078 M 015 21 30.0
12 10 10x10 6.5
Globular Cluster
NGC 7331
22 37.1 34 26 10x3
10.4 Spiral Galaxy b
NGC 7635
23 20.7 61 10 10x5
11.0 Nebula
NGC 0288
00 52.6 -26 36 10x10
7.2 Globular Cluster
NGC 1807
05 10.7 16 32 10x10
7.5 Open Cluster
NGC 6530
18 04.7 -24 20 10x10
6.0 Open Cluster
NGC 6645
18 32.7 -16 54 10x10
9.0 Open Cluster
NGC 4395
12 25.9 33 32 10x8
11.0 Spiral Galaxy
NGC 0663
01 46.0 61 16 11x11
7.0 Open Cluster
NGC 2903
09 32.1 21 31 11x5
9.7 Spiral Galaxy b
NGC 0891
02 22.4 42 41 12x1
12.2 Spiral Galaxy b
NGC 1960 M 036 05 36.2
34 09 12x12 6.3
Open Cluster
NGC 3628
11 20.3 13 37 12x2
10.3 Spiral Galaxy b
NGC 6705 M 011 18 51.1
-06 16 12x12 6.0
Open Cluster
NGC 7654 M 052 23 24.2
61 36 12x12 7.0
Open Cluster
IC 5146
21 53.5 47 16 12x12
10.0 Nebula
IC 1613
01 04.8 02 07 12x11
9.0 Irregular Galaxy
NGC 1513
04 09.9 49 31 12x12
9.0 Open Cluster
NGC 1893
05 22.6 33 24 12x12
8.0 Open Cluster
NGC 6709
18 51.5 10 21 12x12
8.0 Open Cluster
NGC 5907
15 15.9 56 20 12x2
10.4 Spiral Galaxy c
NGC 4631
12 42.2 32 33 12x1
9.7 Spiral Galaxy c
NGC 4244
12 17.5 37 48 13x1
10.7 Spiral Galaxy b
NGC 5904 M 005 15 18.5
02 05 13x13 6.2
Globular Cluster
NGC 0225
00 43.8 61 46 14x14
8.0 Open Cluster
For the next set of objects which goes up to 29 arc minutes, the images are 15 mm with the 12" f10, 10 mm with the 10" f10 and 6.6 mm with the 10" f6.3. These are all good candidates for the ST-8 chip size or possibly for direct 35 mm photography. The largest of them will not fit on the ST-7 chip even with the 10" f6.3. There is also the option of using the 0.63 focal reducer on an f10 or f6.3 telescope to extent coverage to somewhat larger objects. A 1200 mm focal length gives an image for the largest of the objects of 630 pixels. A nice size for the ST-8 chip. Clearly for these larger objects it is time to consider a good telephoto lens mounted directly on the CCD imager. This is not only a good, but a necessary solution as we move to imaging the largest objects with a CCD imager. There are an astonishing 50 objects in this group with 19 of them being M objects.
NGC 0188
00 44.2 85 19 15x15
10.0 Open Cluster
NGC 2682 M 067 08 51.0
11 49 15x15 7.0
Open Cluster
NGC 4565
12 36.4 25 59 15x1
10.5 Spiral Galaxy b
NGC 1817
05 12.1 16 42 15x15
8.0 Open Cluster
NGC 2281
06 49.3 41 04 15x15
6.0 Open Cluster
NGC 6811
19 38.2 46 34 15x15
9.0 Open Cluster
NGC 6809
19 40.1 -30 56 15x15
7.0 Globular Cluster
NGC 2403
07 36.8 65 36 16x10
8.8 Spiral Galaxy c
NGC 7293
22 29.7 -20 51 12x16
6.5 Planetary Nebula
NGC 7790
23 58.4 61 13 17x17
13.0 Open Cluster
NGC 0247
00 47.1 -20 45 18x5
10.7 Spiral Galaxy c
NGC 2447 M 093 07 44.5
-23 52 18x18 7.0
Open Cluster
NGC 3031 M 081 09 55.6
69 04 18x10 8.0
Spiral Galaxy a
NGC 5272 M 003 13 42.2
28 23 18x18 6.0
Globular Cluster
NGC 6656 M 022 18 36.4
-23 56 18x18 6.0
Globular Cluster
NGC 6888
20 12.5 38 25 18x12
? Nebula
NGC 7023
21 02.0 68 10 18x18
? Nebula
IC 0342
03 46 68 06 18x17
9.2 Barred Spiral c
NGC 6664
18 36.7 -08 14 18x18
6.0 Open Cluster
NGC 4258 M 106 12 19.0
47 18 19x6
9.0 Spiral Galaxy b
NGC 4656
12 44.0 32 10 19x2
11.0 Irregular Galaxy
NGC 1039 M 034 02 42.0
42 47 20x20 6.0
Open Cluster
NGC 1912 M 038 05 28.7
35 51 20x20 6.2
Open Cluster
NGC 2024
05 41.9 -01 50 20x20
? Nebula
NGC 2099 M 037 05 52.3
32 34 20x20 6.2
Open Cluster
NGC 2422 M 047 07 36.6
-14 30 20x20 5.0
Open Cluster
NGC 6121 M 004 16 23.7
-26 31 20x20 7.4
Globular Cluster
NGC 6822
19 44.9 -14 46 20x10
10.0 Irregular Galaxy
NGC 7243
22 15.2 49 53 20x20
8.0 Open Cluster
NGC 6809 M 055 19 40.1
-30 56 20x20 7.0
Globular Cluster
NGC 1435
03 46.2 23 45 15x20
6.8 Nebula
NGC 1245
03 14.6 47 14 20x20
9.0 Open Cluster
NGC 6940
20 34.6 28 18 20x20
8.0 Open Cluster
NGC 6791
19 20.8 37 46 20x20
11.0 Open Cluster
NGC 7789
23 57.0 56 43 20x20
10.0 Open Cluster
NGC 0300
00 55.0 -37 42 21x14
11.3 Spiral Galaxy c
NGC 0253
00 47.6 -25 18 22x6
7.0 Spiral Galaxy c
NGC 4236
12 16.7 69 28 22x5
10.7 Barred Spiral
NGC 5457 M 101 14 03.2
54 21 22x20 9.0
Spiral Galaxy c
NGC 6205 M 013 16 41.7
36 27 23x23 5.7
Globular Cluster
NGC 2437 M 046 07 41.9
-14 49 25x25 8.0
Open Cluster
NGC 2477
07 52.3 -38 33 25x25
7.0 Open Cluster
NGC 6405 M 006 17 40.1
-32 13 25x25 6.0
Open Cluster
NGC 6494 M 023 17 56.9
-19 01 25x25 7.0
Open Cluster
NGC 6611 M 016 18 18.8
-13 47 25x25 6.5
Nebula
NGC 1528
04 15.2 51 15 25x25
6.0 Open Cluster
NGC 2546
08 12.4 -37 38 25x25
8.0 Open Cluster
NGC 2264
06 41.2 09 53 15x26
5.0 Open Cluster
NGC 0281
00 53.3 56 35 23x27
8.0 Nebula
NGC 6514 M 020 18 01.9
-23 02 29x27 8.5
Nebula
For the next group of objects, up to 60 arc minutes in size, one must use telescopes with reducers even for 35 mm photography and medium telephoto lenses for CCD chips. There are only 19 objects in this group with 8 being M objects. It is an important group of bright objects of great interest. These objects, because of their size, have great detail and are the focal point of many photographic and imaging techniques. We might note for reference that the moon and sun are about 30 arc minutes, right between this group and the one above.
NGC 2168 M 035 06 08.8
24 20 30x30 5.5
Open Cluster
NGC 2287 M 041 06 47.0
-20 45 30x30 6.0
Open Cluster
NGC 7092 M 039 21 32.2
48 26 30x30 5.0
Open Cluster
IC 0405
05 16.2 34 16 30x19
6.0 Nebula
NGC 0869
02 19.0 57 09 35x35
4.4 Open Cluster
NGC 0884
02 22.4 57 07 35x35
4.7 Open Cluster
NGC 6634 M 025 18 31.7
-19 15 35x35 6.0
Open Cluster
NGC 0055
00 15 -39 13 25x40
7.8 Irregular galaxy
NGC 2244
06 32.4 04 52 40x40
5.5 Open Cluster
NGC 2548 M 048 08 13.7
-05 47 40x40 5.5
Open Cluster
NGC 1647
04 46.1 19 05 40x40
6.5 Open Cluster
NGC 1977
05 35.5 -04 52 40x25
7.0 Nebula
NGC 2174
06 09.7 20 30 40x30
? Nebula
NGC 0752
01 57.8 37 41 45x45
7.5 Open Cluster
NGC 6618 M 017 18 20.9
-16 11 45x35 6.0
Nebula
NGC 1746
05 03.6 23 48 45x45
6.0 Open Cluster
Sh2-155
22 56.8 62 37 50x10
7.7 Nebula
NGC 0598 M 033 01 33.9
30 39 60x60 5.3
Spiral Galaxy c
NGC 6475 M 007 17 54.0
-34 49 60x60 5.0
Open Cluster
The final group of objects are definitely 35 mm candidates but can be imaged with a CCD chip if an appropriate focal length telephoto lens is used. For example, a 400 mm telephoto lens will fit objects of 60 arc minutes on the ST-8 chip. This group holds the really giant objects, those well over 1 degree in size. To fit M 31 on an ST-8 chip requires a focal length of only 180 to 200 mm. There are only 12 objects in the giant object group but 6 are well known M objects.
NGC 1976 M 042 05 35.4
-05 23 65x65 4.0
Nebula
NGC 6960
20 45.7 30 43 70x6
8.0 Nebula
NGC 6992-5
20 56.4 31 42 78x8
8.0 Nebula
NGC 2237-9
06 32.3 05 03 60x80
9.0 Nebula
NGC 2632 M 044 08 40.4
19 41 80x80 4.5
Open Cluster
NGC 6523 M 008 18 04.7
-24 20 80x40 5.0
Nebula
NGC 6603 M 024 18 18.4
-18 26 60x90 4.5
Open Cluster
M 045 03 46.9 24 07
100x100 1.4 Open Cluster
NGC 7000
20 58.8 44 20 100x100
5.0 Nebula
NGC 1499
04 3.4 36 25 145x40
6.0 Nebula
NGC 0224 M 031 00 42.7
41 16 150x50 4.0
Spiral galaxy b
IC 1396
21 39.1 57 30 140x170
Nebula
As I review this list, I wonder at the great variety and size of the non-stellar objects in the sky. Looking at the distribution of the Messier objects among them I wonder at how Messier saw some of them at all and how he missed others. It is a wondrous list. The list also demonstrates the difficulty of imaging all of them with a single telescope or camera. Just on the basis of size, it becomes clear that one selection of optics or one imager will not capture all of them equally well. In fact the range is so great that if imaging is a goal, the selection of the base telescope will have to be adjusted to cover with facility the range of objects of greatest interest.
In the following example, covered in some depth, I assume that an ST-7 sized chip is used and a 10" f6.3 telescope is chosen as the basic optic. The 10" f6.3 telescope has a focal length of 1600 mm. If one assumes that this can be extended or reduced with adapters from a 2X Barlow to a 0.50 field reducer, the focal lengths and speeds become, 3200 f12.6 to 800 mm f3.2 That range is probably a bit optimistic if one expects to maintain optical quality. But a range of 2200 mm f8.8 to 1000 mm f4.0 is possible with reasonably good image quality. Considering now that one wants to fill the chip with the 1000 mm focal length and have an image no smaller than about 100 pixels at 2200 mm, it is possible to image a range of objects from 20 arc minutes down to 1.5 arc minutes. This setup, with the criteria stated, encompasses 236 of the objects and 84 of the Messier objects. Left out are the 31 (4M) very smallest objects and the 46 (M21) very largest. The range of objects can be shifted upward in size by using the ST-8 chips size.
For the very smallest objects one has to go to a longer focal length. This could be accomplished with a 12" f10 (fl = 3000 mm) or with the 10" f6.3 with a 2X field expander (Barlow) (3200 mm). It is hard to magnify the smallest objects much more because of atmospheric seeing limitations that are around 1 arc second. For the very largest objects, a good telephoto lens is quite suitable. Focal lengths of 400 to 500 mm at f2.8 are not uncommon. The 500 mm lens is good for objects of 40 arc minutes size and smaller and a 200 mm lens will take in objects of 100 arc minutes on the ST-7 size chip. Thus the large objects can be taken care of with a set of telephoto lenses. The telescope is needed to reach down to the smaller objects while retaining reasonable light gathering power.
I have not held really tight specifications on my criteria for "filling the chip." The reasoning is that there are a variety of chip sizes, pixel sizes and exact dimensions for the chips which might be used. I currently use the ST-7 and ST-8 which have the Kodak 0400 and 1600 chips respectively. It is rectangular so if you consider an image which is sort of oval, you might get it on the chip by rotating the imager to fit the long side to the long axis of the object. I do not like to rotate the imager and the focal length steps are rather large in any case. So, I simply assumed an equivalent circular image and an approximate fit of the image to the chip. You may want to adjust the ranges a bit to fit your idea of how tightly you want to fit the image to the chip. I think the list gives the general concept of how to proceed. Now that I have the ST-8 I use it almost exclusively since I get the same resolution as the ST-7 and four times the imaging area.
Books which discuss many aspects of astrophotography are listed in the Bibliography/Applications section on this web site.