Do you need a large scope to view nebulae?

[RobH]

All things being even, visually you want as much aperture as possible with a low focal ratio...F4-F5 or so.

As for refractors being better on some nebulae.....only the very large ones, and something like the rosette is of such a low surface brightness that I doubt much would be visible with a smallish 'frac.

Also, this is nothing to do with the scope design, just the FOV.

Try looking at M42 with a good eyepiece through an F5 20 inch.....you can't get all of it in the FOV, but what you can see is spectacular, and you are allowed to pan the scope

F10 SCT's......Olly, we have very different experiences here

Last week, when setting up my new 11 inch Edge SCT, I used the supplied 23mm Axiom eyepice and could fit the whole of the moon into the FOV, so no tunnel vision there, and a very bright and crisp image too.

Cheers

Rob

[nightvision]

For decades I have been a casual and occasional astronomer, only recently having access to more time, equipment and..... frustration.

For me the greatest single astro experience was having no equipment while visiting family in France. Staying in a very dark area and seeing more with my naked eye in one night than I believed possible. I know that upgrading my scopes and eyepieces could never compete. I have never managed to re-capture that experience (came close in the Scottish Highlands last year), conclusion: Equipment no matter how good gets truly battered by LP and conditions and almost equalised.

I am not giving up on interesting smudges, knowing photons from M82 have taken over 10 million years to get here compensates for the lack of visual spectacle, its more in my head.

As others have said, consider getting out of town.

I have seen the LP in Holland first hand so I know it won't be easy to find somewhere dark.

[ollypenrice]

All things being even, visually you want as much aperture as possible with a low focal ratio...F4-F5 or so.

As for refractors being better on some nebulae.....only the very large ones, and something like the rosette is of such a low surface brightness that I doubt much would be visible with a smallish 'frac.

Also, this is nothing to do with the scope design, just the FOV.

Try looking at M42 with a good eyepiece through an F5 20 inch.....you can't get all of it in the FOV, but what you can see is spectacular, and you are allowed to pan the scope

F10 SCT's......Olly, we have very different experiences here

Last week, when setting up my new 11 inch Edge SCT, I used the supplied 23mm Axiom eyepice and could fit the whole of the moon into the FOV, so no tunnel vision there, and a very bright and crisp image too.

Cheers

Rob

Yes, I get half a degree in the Meade 10 inch with the standard Plossl but the 10 inch Meade gives almost exactly the same FOV as the 20 inch F5 Obsession. Now some 'boxing in' is to be expected with a half metre scope but I just feel it comes a bit early in an SCT with a quarter of the light grasp. In a fast 10 inch Newt you could expect aboput 2.7X the field of the Meade. That is what I mean by 'tunnel vision'.

I think I come across as a bit of an SCT basher but that is not really the case. I just think that they are over marketed and often chosen unwisely. (I chose unwisely myself.) The C11 Edge is 'on my list' for longer FL imaging once I can be sure to get a reducer to work with it. I'm sure you'll get cracking results because the optics look great on Serge's images.

From a dark site a small refractor has no trouble with the Rosette or the whole of the Veil complex. I used to revel in both when I had the Genesis and was thrilled to bits to find the 70mm Pronto could also show them clearly enough for beginners to see. (2 inch EP/Baader O111 visual filter.) As much aperture as possible without letting the focal length get much above 500mm is the key, I think. And a dark site!

Olly

[RobH]

I think you've really hit the nail on the head Olly.....a dark site is the key!

Talking Edge scopes and focal reducers, as an experiment, I tried my celestron f6.3 reducer flattener asnd the results were pretty awful!

A mate in the US has an Astrophysics CCD67 (or whatever it's called!) for me, and I will be seeing him early next month....apparently they work OK so I'm looking forward to having a go with it.

Cheers

Rob

[michael.h.f.wilkinson]

The long FL of a big SCT cannot be overcome by any EP, however wide its field.

It can be mitigated but you will still be boxed in. You have to decide what is the smallest field you can tolerate. I find our 10 inch SCT pretty frustrating in terms of FOV, I must say. It is convenient in other ways but has dire tunnel vision. Why have ten inch f10 when you can have 10 inch F6? The gain on the planets is more theroetical than real.

Ollyu

I beg to differ. F-ratios are mainly an issue in DSO photography (VERY IMPORTANT THERE!!) and in wide-field objects. For the vast majority of DSOs large FOV is not needed. I get 1.38 deg FOV at exit pupil 4mm with my SCT. This is plenty for all but the most extended DSOs. For extended objects, I have bins and the little 80mm F/6. For a given aperture, and a given magnification, the view will be essentially the same regardless of the optical design (light-throughput differences aside). It does not matter whether I use a 11 mm Nagler in an F/5 dob or a 22mm Nagler in an F/10 SCT of the same aperture. Both yield the same diameter exit pupil with the light rays from different parts of the image coming out at the same angle. Any observed differences must be down to differences in transmission (e.g., central obstruction), but these effects amount to perhaps 1-5% difference in brightness. It is true that with a 21mm ethos in an F/5 dob, I get a much larger field of view than with the equivalent 42 mm SWA in an SCT.

Having spotted 77 galaxies in one month with my C8 shows how powerful the compact SCT is. The killer feature is that I can plonk the C8 in the back of even a modest car, whereas a dob might cause more difficulties (especially on holidays, when we also have to pack the tent, clothes, kids toys, ten pairs of shoes for the missus , etc). This has meant I could take my little 8" to darker sites. This to appease the emperor .

I could of course get an 8" F/5 in a car, but now lets go to the bigger end: A C14 can be transported in my car with room to spare (pain to set up and on the wallet , but possible), but a 14" F/5 dob would be a problem (flextubes help, but still not easy).

Bottom line: focal ratio is important for wide field and photography, but for getting most fuzzies visually, speed is not essential.

[ollypenrice]

I think you've really hit the nail on the head Olly.....a dark site is the key!

Talking Edge scopes and focal reducers, as an experiment, I tried my celestron f6.3 reducer flattener asnd the results were pretty awful!

A mate in the US has an Astrophysics CCD67 (or whatever it's called!) for me, and I will be seeing him early next month....apparently they work OK so I'm looking forward to having a go with it.

Cheers

Rob

Excellent news. The Celestron Edges are the most convincing SCTs to my mind. I can imagine special occasions, too, for imaging at F10. Are you going to use an aftermarket focuser?

Olly

[ollypenrice]

I beg to differ. F-ratios are mainly an issue in DSO photography (VERY IMPORTANT THERE!!) and in wide-field objects. For the vast majority of DSOs large FOV is not needed. I get 1.38 deg FOV at exit pupil 4mm with my SCT. This is plenty for all but the most extended DSOs. For extended objects, I have bins and the little 80mm F/6. For a given aperture, and a given magnification, the view will be essentially the same regardless of the optical design (light-throughput differences aside). It does not matter whether I use a 11 mm Nagler in an F/5 dob or a 22mm Nagler in an F/10 SCT of the same aperture. Both yield the same diameter exit pupil with the light rays from different parts of the image coming out at the same angle. Any observed differences must be down to differences in transmission (e.g., central obstruction), but these effects amount to perhaps 1-5% difference in brightness. It is true that with a 21mm ethos in an F/5 dob, I get a much larger field of view than with the equivalent 42 mm SWA in an SCT.

Having spotted 77 galaxies in one month with my C8 shows how powerful the compact SCT is. The killer feature is that I can plonk the C8 in the back of even a modest car, whereas a dob might cause more difficulties (especially on holidays, when we also have to pack the tent, clothes, kids toys, ten pairs of shoes for the missus , etc). This has meant I could take my little 8" to darker sites. This to appease the emperor .

I could of course get an 8" F/5 in a car, but now lets go to the bigger end: A C14 can be transported in my car with room to spare (pain to set up and on the wallet , but possible), but a 14" F/5 dob would be a problem (flextubes help, but still not easy).

Bottom line: focal ratio is important for wide field and photography, but for getting most fuzzies visually, speed is not essential.

I don't think we really disagree, Michael. I find I do want more than a degree and a half quite often. This is the point I was aiming to make, to quote you;

It is true that with a 21mm ethos in an F/5 dob, I get a much larger field of view than with the equivalent 42 mm SWA in an SCT.

I rather overstated it by referring to 'dire tunnel vision' and should have been more temperate in my wording! Apologies.

I seem to be a widefield junkie at the EP as well as at the camera because I do like to see as wide as possible. That's probably why I don't really get on with the SCT so well.

Olly

[michael.h.f.wilkinson]

I don't think we really disagree, Michael. I find I do want more than a degree and a half quite often. This is the point I was aiming to make, to quote you;

It is true that with a 21mm ethos in an F/5 dob, I get a much larger field of view than with the equivalent 42 mm SWA in an SCT.

I rather overstated it by referring to 'dire tunnel vision' and should have been more temperate in my wording! Apologies.

I seem to be a widefield junkie at the EP as well as at the camera because I do like to see as wide as possible. That's probably why I don't really get on with the SCT so well.

Olly

Fair enough. My SCT is not that big, and I still get 7 galaxies in one FOV in Virgo, but with a bigger SCT I might lust for wider views (I am also looking at the option of a Dob).

My main point is: do not follow the "DSOs require fast scopes"-line. This is repeated rather too often. Given that many DSO observers (with F/4.5 - F/5 dobs) claim the 13mm ethos or 11-13mm Nagler is the most used EP, switching to a 21mm ethos or 22 to 26mm Nagler is not such a big deal, and will give identical views. This despite the fact that the image in the focal plane of the F/5 is indeed brighter. People often do not appreciate that by using different EPs, you magnify less with the SCT, which compensates completely for this effect.

What is true is that the stock 1.25" visual back of the C8 is a pain, and boxes you in. The Baader 2" back I fitted was a breath of fresh air, in that respect. I can now get the double cluster or the Pleiades in one FOV.

[RobH]

Excellent news. The Celestron Edges are the most convincing SCTs to my mind. I can imagine special occasions, too, for imaging at F10. Are you going to use an aftermarket focuser?

Olly

It is much crisper than my old Meade was Olly.

With the 8300 chip, even at F10 the FOV is good (my post about flats showed an unprocessed NGC2903, so you get the idea)

I immediately added a moonlight SCT focuser with robofocus, that I used to have on my meade. I do think something like this is essential for imaging with one of these.

Cheers

Rob

[chiltonstar]

After reading these posts, I had a try with my Mak 127 using a 40mm EP (Omni) on some popular nebulae on a reasonably clear night (last night). I was surprised by how bright M51 was, for example, with quite a lot of detail using averted vision. There was also some detail in M101, which I've only seen before in a much larger scope. I set my ED80 up alongside for a quick comparison and it has to be said that despite it having a much faster f ratio, the Mak beat it hands down in terms of brightness and detail. Limiting visibility here last night was about mag 5.2.

I shouldn't be surprised I suppose, as the visual descriptions of all the Messier objects in "The Messier Album" by Mallas are all with a long focus 4" refractor - same f ratio as the Mak but 16/25 "ths" of the light!

Chris