Fast imaging scopes?

[rocketandroll]

Hi all

Ok, so, admitting to myself I am addicted is the first step right? :-)

Having taken my first steps into DSO-imaging this last couple of months (with the help and advice of the locely people on SGL I hasten to add) I am now starting looking longer term at what equipment I should actually start looking at getting.

I have used my Meade 127mm Apo loads, and my 80ED DS Pro hardly at all, but only because I've not done anything that has needed anything particularly wide-field yet.

I am quite happy with the idea of effectively having two set-ups, one for wider field stuff, and one for smaller objects, galaxies, planetary nebulae etc.

The Meade is great... but given the fact it looks likely that much of my imaging for the next couple of years will be done 'on the fly' at sites where I will need to set up quickly, get imaging and gather as much data as possible as fast as possible (eg: at star parties) I am seriously looking at faster scopes.

If I want a similar (or smaller) FOV as the Meade, but want to at least double the speed (it's f7.5, so f5.something?) Am I really looking at reflectors rather than refractors?

I keep coming back and drooling over the f2.8 Boren-Simon 'PowerNewt's... £1700 or so at the current exchange rate isn't bad at all.... and means I could gather the equivalent of over an hours worth of data from the Meade in 10 minutes!!!

Are there any other good options I should be looking at in that sort of performance range... if I don't want to start spending four or five grand on a scope :-)

Anyone got any recomendations?

Ben

[rocketandroll]

...actually, mods, just wondering if this should be in equipment help rather than discussion? feel free to move it if you feel this is in the wrong place.

Ben

[michael.h.f.wilkinson]

Newtonians, and fast ones even more, need careful collimation. A fast apo does not. If you want to set up quickly, and get data quickly, consider a focal reducer on your Meade 127, or a fast refractor.

[rocketandroll]

I know that reflectors require collimation, but assuming it was moved everywhere in a well padded case, would it really need it EVERY time it was set-up? I've heard most people say that collimation is only really needed if the scope gets a knock?

Taking those Boren-Simon newtonians as an example, they claim to drive them around in the back of a jeep across the desert and not need collimation afterwards?! :-) I know sales talk is not necessarily to be taken at face value, but a lot of imagers seem to use reflectors at star parties with no lengthy delays?

Hmmm... are there any significantly faster refractors about in the 120mm+ range? Seems the highest I can find is f5.6 or so, at about double the price of one of those Newtonians.

The whole collimation thing does worry me a bit in general, that's why I started out with refractors :-)

Ben

[lukebl]

Newtonians, and fast ones even more, need careful collimation.

True, but my Newtonian hasn't needed collimating since last September, despite every effort by me to un-collimate it by dropping ladders on it, walking into it in the dark, bashing chairs against it, and having a goose accidentally fly into it! I guess I must be lucky.

[michael.h.f.wilkinson]

My old 6" F/8 rarely if ever needed collimation, but I always put that down to (i) a sturdy mirror cell design, and (ii) being F/8. BTW, have you considered the Fastar SCTs? The 8" Edge OTA of Celestron is a lot cheaper than he Boren 8" F/2.8 astrograph, and reaches F/2 (but needs a suitable CCD like the Starlight Xpres, rather than a DLSR)

[rocketandroll]

Cheers all

Yeah, my other option is looking at other large-ish reflectors with focal reducers/flateners to increase the speed. I really want to stick with DSLR imaging for now if I can.

Dunno really, haven't found any 3rd party reviews of the BS powernewts anywhere, which is always a bit of a worry... I always like to see some end-user's opinions on such things.

The MN190 is another option, though dunno if you can make that even faster than the f5.3 it comes at?

I'm really after something with the magnification for galaxies and smaller DSO's with some real speed to it as imaging opportunities for me are always so short.

I may well be asking the impossible without a massive budget :-)

Ben

[michael.h.f.wilkinson]

Cheers all

Yeah, my other option is looking at other large-ish reflectors with focal reducers/flateners to increase the speed. I really want to stick with DSLR imaging for now if I can.

Dunno really, haven't found any 3rd party reviews of the BS powernewts anywhere, which is always a bit of a worry... I always like to see some end-user's opinions on such things.

The MN190 is another option, though dunno if you can make that even faster than the f5.3 it comes at?

I'm really after something with the magnification for galaxies and smaller DSO's with some real speed to it as imaging opportunities for me are always so short.

I may well be asking the impossible without a massive budget :-)

Ben

For a not quite massive but still SERIOUS budget, look at this 8" F/3 monster

(description only in German I am afraid)

[ollypenrice]

This is a very hard one. Fast reflectors, I am sure, will indeed need collimating carefully evey time if moved. This is true of the Takahashi Epsilons I have seen working at my place. There is a huge difference between F3 and F4 or F5 in this regard. There are the mechanical issues as well. Orthogonality needs maintaining to a high order. The Mak Newt does well but folks on here say it is not easy and needs careful setting up, which I guess must sometimes eat into imaging time. Focus is also critical.

With all these fast reflector systems they are photon magnets when fine tuned and in good fettle. When not they are disappointing. This seems true of one obvious choice, the Hyperstar. You see great images and frankly poor ones depending on whether the imager got the fickle sytem up to speed or not. No free lunch!

I was talking to a well known European imager the other day. Not short of a bob or two he has tried a fair few astrographs at the high end and had an awful lot of problems with some of them, so the ads don't always deliver.

I love our Tak FSQ85 and it does come in at less than 4K. It can work at F3.9 or F5.3, both very nice thank you! It is easy to focus and mechanically like a cross between a Swiss watch and a tank. In all the time I have been using it it has wasted precisely no imaging time whatever. Plug and play. But you want more FL, I know. However, the long FL Galaxy Season is soon over.

Borg astrographs?

And as a Canon user, a 200L lens and Telescope Service microfucuser would be on my list if I were you. Fast, flat widefield images at under F3... I hook one up to a CCD.

Olly

[shaunster]

Having seen the results from the orion optics astrographs they look very nice and better than anything else ive seen!!

Of course they are very expensive

[Whippy]

For a not quite massive but still SERIOUS budget, look at this 8" F/3 monster

(description only in German I am afraid)

Intes Micro also do some modified maks that operate at f3, they look pretty serious as I assume the price would be. There's also the MN74 which is a 7" f4 Mak-Newt astrograph, something I've long wanted!

Another thing to take into account is that filters are normally designed to work at around f4 and up so you can get issues in that respect should you use something that fast.

Tony..

[Merlin66]

I've got a 6" f3.5 Schmidt Newtonian - Meade Cometracker I bought back in 1985.

I gives fantastic wide fields with good definition.

There must be something similar available today???

[step_hen]

] There's also the MN74 which is a 7" f4 Mak-Newt astrograph, something I've long wanted!

Tony..

I'd LOVE one of those! My Meade SNT is 10" and F4. Its very sensitive to poor collimation and is useless in any kind of wind, its like a great big sail, and then there is the flexure problem....

I could go on!

Stephen

[Whippy]

Problem with the 74 is that they're rare as rocking horse droppings, especially in the UK unfortunately.. Same goes for the IM f6 'photo' maks, all the plusses of the MN's with the advantage of the camera at the back, not in the awkward places the newts occasionally have .

[rocketandroll]

hmmmm... maybe I should just be looking at a slightly faster refractor then? For the same reson I chose a refractor in the first place. This has all done a lot to put me off reflectors in general :-)

What sort of speed increase do I get going from f7.5 to f5.5 for example? I forget the calculation but off the top of my head, are we talking about twice as fast?

Are there any f5.something refractors over 110mm diameter around for under £2K? Or am I looking at a long wait and the second hand market?

Ben

[michael.h.f.wilkinson]

hmmmm... maybe I should just be looking at a slightly faster refractor then? For the same reson I chose a refractor in the first place. This has all done a lot to put me off reflectors in general :-)

What sort of speed increase do I get going from f7.5 to f5.5 for example? I forget the calculation but off the top of my head, are we talking about twice as fast?

Are there any f5.something refractors over 110mm diameter around for under £2K? Or am I looking at a long wait and the second hand market?

Ben

the speed increase is the square of the ratio: (7.5/5.5)^2 = 1.86, so a nearly twofold speed increase. The cheapest way to get F/5 or thereabouts is using a focal reducer. This does reduce the usable image circle, but the objects you are gunning for are not extended.

I am not sure you should ditch the idea of catadioptric scopes. The Mak newts (Bresser 6" and Skywatcher MN190) and Schmidt newts (Meade LXD75 series) of are much more affordable at 6 or 8" or even 10" than any APO, and come in speeds of F/4 and F/5 or F5.3. Yes you may need some collimation, but if you look at the cost of a say 127mm APO F/6 (WO) of 3600+ euro, I wonder if that expense is worth it.

[rocketandroll]

the speed increase is the square of the ratio: (7.5/5.5)^2 = 1.86, so a nearly twofold speed increase. The cheapest way to get F/5 or thereabouts is using a focal reducer. This does reduce the usable image circle, but the objects you are gunning for are not extended.

Forgive my ignorance on such things... but does a focal reducer reduce the field of view (ie: crop the outer edges off) and/or does it actually reduce the apparent size of the object being imaged, ie: reduce the apparent magnification?

I can cope with the former, but probably not the latter, as I really want, if anything, to get larger images of smaller objects.

Might have a look at the LXD75 series too... are those speeds on those achieved with reducers/flatteners or is that 'as standard'?

Thanks again all for the advice.

Ben

[rocketandroll]

Oh, one other quick question.... the LXD75's all seem to only be available with a mount, tripod, goto etc.... are they available as an OTA anywhere?

Ben

[michael.h.f.wilkinson]

Oh, one other quick question.... the LXD75's all seem to only be available with a mount, tripod, goto etc.... are they available as an OTA anywhere?

Ben

I looked for separate OTAs, but the best I can get is a Bresser-labeled 6" F/5 OTA (I think a Meade clone/rebadge), which is pretty decent, but the (heavier, more capable) MN190 is just a bit more expensive.

A focal reducer reduces the focal length of a scope. This reduces the image size, but putting a 0.7x focal reducer on an F/7 scope gives you an F/4.9 scope of the same aperture and same (or slightly smaller) true field of view. Getting a 127mm F/7.5 apo with a focal reducer yielding about F/5 is a lot cheaper than getting a 127 F/5 of decent quality, and both give the same image scale.

A focal reducer does not crop, but reduces the diameter of the image circle by the same amount as the reduction in focal length. I can reduce my F/10 C8 to F/6.3 (or even F/3.3, but with a tiny image circle) using a focal reducer.

[rocketandroll]

Thanks for all the advice Michael!

Just looking at all options...

what about something like this:

Ritchey-Chrétien telescope 8",f/8 RC Astrograph on eBay (end time 02-May-11 11:38:40 BST)

With a focal reducer? Would a focal reducer designed for an SCT type scope work with this?

Dunno if I'm totally barking up the wrong tree? :-)

Ben

[Whippy]

The reducer/flatteners designed for SCT's won't work with the RC because they already have a pretty (but not totally) flat, coma free field which the SCT reducer/flattener corrects. Basically you'd end up with an over-corrected field that has coma intrduced. In other words not great!

What the RC's need is a reducer that doesn't flatten like the range made by Intes Micro and Optec. I tried using my WO FFII on my 6" RC and it worked but my camera has a relatively small chip compared to DSLR's so I couldn't say whether the entire FOV would be useable.

Tony..

[rocketandroll]

And as a Canon user, a 200L lens and Telescope Service microfucuser would be on my list if I were you. Fast, flat widefield images at under F3... I hook one up to a CCD.

Olly

Olly...

As I was also looking at doing imaging with a lens later this year (want to try and get Andromeda in a single shot)... what do you recon to the potential success of something like this:

CANON FD MOUNT F2.8/200MM PRIME TELEFOCUS LENS: SUPERB! on eBay (end time 10-Apr-11 21:34:57 BST)

With an adapter on the Eos?

200mm primes for Eos fit are all mental expensive :-) Saw one at f1.8 on ebay for almost £4K!! :-) Would be lovely though, at that speed you could get a lovely widefield in a single 1min exposure :-)

Ben

[rocketandroll]

The reducer/flatteners designed for SCT's won't work with the RC because they already have a pretty (but not totally) flat, coma free field which the SCT reducer/flattener corrects. Basically you'd end up with an over-corrected field that has coma intrduced. In other words not great!

What the RC's need is a reducer that doesn't flatten like the range made by Intes Micro and Optec. I tried using my WO FFII on my 6" RC and it worked but my camera has a relatively small chip compared to DSLR's so I couldn't say whether the entire FOV would be useable.

Tony..

Thanks Tony

Do you have any links/advice on who stocks those reducers and who I might be able to get some advice from on whether they'd work with a given scope?

Don't want to spend a wad of cash then find it won't work :-)

Many thanks again all for your help and advice!

Ben

[Whippy]

I was told by Wolfi at telescope service when I purchased my 6" that the Intes Micro 0.8x and 0.6x reducers should work well on the RC's, the Optec ones should do the same job but I'm not sure who stocks them.

Tony..

[ollypenrice]

Olly...

As I was also looking at doing imaging with a lens later this year (want to try and get Andromeda in a single shot)... what do you recon to the potential success of something like this:

CANON FD MOUNT F2.8/200MM PRIME TELEFOCUS LENS: SUPERB! on eBay (end time 10-Apr-11 21:34:57 BST)

With an adapter on the Eos?

200mm primes for Eos fit are all mental expensive :-) Saw one at f1.8 on ebay for almost £4K!! :-) Would be lovely though, at that speed you could get a lovely widefield in a single 1min exposure :-)

Ben

Couldn't open the link I'm afraid but my EF200L was 500 pounds second hand from LCE. I like it. This was with Atik 4000 CCD cameras, OSC and mono for Ha.

Olly