Aperture

[Craig20264]

With my interest for AP growing, I am keen to get some decent use out of my DSLR. I think I have a decent enough camera to set me on the road. It's a Nikon D5100. It has live view, a movable/tiltable screen, High ISO noise reduction and Long exposure noise reduction can both be disabled.   I have had limited success due to lack of tracking so I plan to invest in the Skywatcher EQ5 PRO Synscan GOTO mount to mount the DSLR on.

 Eventually the inevitable question of a scope for imaging will rear its head, and I would ideally like to drop a 200 Reflector on the mount. However, I've read that this mount is probably past it's limit with the weight of the 200. So with this in mind maybe the 150 would be a better option.  

My question is. Is aperture such a big factor with imaging as it is with observing? And maybe i'm barking up the wrong tree with scope choice, or indeed mount choice, and something else, refractor etc would be more suited? I really am in the dark with this, if you'll excuse the pun, so any pointers are gratefully accepted. My copy of "Making Every Photon Count" is on Santas sleigh already i'm told.    

I would rather wait until the budget suits the job, rather than buy and be disappointed.   

[Phil-lost!]

Hi there, Ive got a nikon d5000 and the tilting screen is a godsend for imaging. I also used to use my 200p on an eq5 and i did have to throw about half the subs away. Have you considered the 130pds? Some stunning images on here and probably be ok on an eq5.

[steppenwolf]

AP is a complex equation but sooner or later the realisation that the mount is the single most important component will hit home! If imaging really does appeal, don't buy twice, get the right mount now and also start with a smaller telescope to get a double whammy! Try to stretch to an HEQ5, there is a remarkable difference between an EQ5 and an HEQ5 although even the latter will be challenged for long exposures with an 8" reflector and the attendant camera and autoguiding paraphernalia.

Many imagers start off with a much smaller telescope, an 80mm Refractor or indeed, a 130mm Reflector as these can make for an excellent system when paired with the right mount.

Welcome to the slippery slope that is the 'dark side' ..............

[Craig20264]

Thanks guys. This is indeed the crux of the issue, or will be at some point. I guess I'm asking whether or not aperture is that important to imaging? If it is, then I need to plan for the future, even though initially the mount will only  be carrying a DSLR, and get the right mount that will be fit for the scope. I must say, an 80mm refractor does seem very inviting, but again, will this leave me wanting more!

[D4N]

Aperture on its own is almost irrelevant to imaging. I say almost as if your aperture is too small the Dawes limit will kick in and you won't be able to resolve up to your pixel scale.

What is important is focal ratio, a high focal ratio will make imaging very slow. A very low focal ratio will also make things difficult as the critical focus zone gets smaller and any issues with the optics become obvious. Even the filters can start to cause issues in very fast scopes.

A focal ratio of 5-7 is easy to image with, under 5 will require well tuned optics and fine focusing but if done well will provide quicker results, 7-10 will be quite time consuming and over 10 is really only useful for solar system objects.

Focal length plays a big role in determining your image scale and field of view, shorter focal lengths are also much easier to track and guide.

An 80mm frac should give a good field of view when combined with a DSLR, there are lots of big DSO's out there to image.

/Dan

Sent from my iPad using Tapatalk

[dph1nm]

Aperture is important, but it depends somewhat on what you want to image. If you are interested in large nebulae etc then a small-ish aperture short FL scope is an ideal instrument. If 14th mag galaxies are your thing then you will probably want something in the 8-12 inch range.

NigelM

[ollypenrice]

85mm aperture:

Aperture, focal length, focal ratio, pixel size, tracking accuracy - they all matter but not in isolation from each other. As Steve said, it's a complex equation. Do yourself a favour and start with a short focal length! The main thing is, you'll have success and enjoy it.

Olly

[Physopto]

If you can try for a second hand EQ6 and second hand frac at about 80 to 90mm. Good condition very important. Olly's photographs are superb and most of us strive to get there. An EQ6 will give great results even on longer focal lengths as long as you are careful and it is well looked after. It can handle quite a weight. If you try it with a physically large scope any wind will be a problem, whereas an 80mm frac will provide less wind surface to screw things up. It is never an easy choice when starting out. Read up, ask questions and if possible join a club and see what others have before making your final choices. Even then very few of us get it right first time.

Best of luck.

Derek

[Craig20264]

Some great info there for me to chew over. Many thanks for replying. I really do appreciate the advice. The information regarding focal length is all new to me, so some studying to be done before a scope is purchased. The mount advice seems to concur with my own thoughts, in as much as the purchase needs to be future proof, so as not to limit my scope choice later on.

[michael.h.f.wilkinson]

Once you read "Making every photon count" you will get a much better idea of what you need. I got mine early (Dutch "Sinterklaas" feast of December 5), and will study it carefully before making any serious forays into DSO imaging.

[ronin]

One way of looking at it is that the William Optics Star 71 is a well regarded imaging scope, seems that quite a few here have acquired one.

The 71 refers to the 71mm aperture.

Aperture is a factor but as somewhat of a generallity it is not the most significant aspect, maybe not even very high.

Would be interesting to set up a poll and see what order people consider the scope parameters should be ordered in for AP.

[ollypenrice]

Here's the thing about focal length: 1) the longer it is the more your field of view is restricted on a given size of chip. This can be good or bad. If you are imaging a small object it will be captured in more detail. If you are capturing a large one it won't fit! 2) the longer the FL for a given chip the fewer arcseconds of sky land on your pixels. This is good if your guiding accuracy and the stability of your seeing will allow this resolution to be realised. That is very often a big 'if!' A common setup which violates this principle is the small pixel DSLR in the long FL SCT. It can take a picture but since it is not operating at a workable pixel scale the field of view is needlessly limited (because you could get the same real resolution at a shorter FL) and the capture is needlessly slow (because each pixel receives too little light.)

One thing's for sure, a DSLR needs a fast F ratio and a short focal length to work productively.

Olly

[michael.h.f.wilkinson]

Which is why I have chosen an APM 80mm F/6 with Tele-Vue TRF-2008 0.8x reducer for my first attempts with the modded EOS 450D. Some short exposures without guiding showed promise.

[Tommohawk]

Some great info there for me to chew over. Many thanks for replying. I really do appreciate the advice. The information regarding focal length is all new to me, so some studying to be done before a scope is purchased. The mount advice seems to concur with my own thoughts, in as much as the purchase needs to be future proof, so as not to limit my scope choice later on.

I agree regarding future proofing, but of course you will never find one scope that's perfect for all targets. Even if you decide to major on say, DSOs, there are big variations in size.

Have just gone through this myself and this is my - possibly dodgy - thinking

A fast scope with gather more light so give you a faster image - as Olly says thats especially usefull with DSLRs which are slower than CCDs. But if you have a fast scope with a small aperture, you will also have a shorter focal length - which is great for a wider field target, eg M31 or M33, but hopeless for a smaller target eg M57. Put another way, there's no point in having a fast scope which is imaging lots of sky that you're not interested in.

That said, it's worth bearing in mind that with a DSLR your sensor resolution will exceed your screen resolution by a factor of about 3, so you can crop images without losing resolution on your screen.

You also need to bear in mind that if you opt for a small aperture refractor, you will be limiting your optical resolution - which would make imaging planets difficult. 

Personally, I think that in terms of bang per buck, a 150PDS or 200PDS is a bargain, or superfast Quattro type F4.

Summary of options:

Small fast apochromatic refractor - lightweight, compact, portable, good for wide range of moderate size DSOs, not so good for planetary or small DSOs and not cheap.

Fast newtonian - faster and cheaper than most refractors, good for smaller DSOs (mosaic required for larger DSOs) options for planetary, but bulkier, longer focal length so more demanding for guiding.

Or of course just get a longer camera lens - which is what I've just done.

[Craig20264]

Some great input there. Thank you all again.

I have just been comparing the EQ6 Syntrek and the HEQ5 Pro Synscan. There is a whopping 7kg difference in recommended imaging weight. 18kg v 11kg. I think it's a no brainer really for an extra £90 new. (unless of course there are other factors at play, like smoothness of tracking etc). Both seem a bit excessive for my humble DSLR, but will be there for the future.

[Tommohawk]

Some great input there. Thank you all again.

I have just been comparing the EQ6 Syntrek and the HEQ5 Pro Synscan. There is a whopping 7kg difference in recommended imaging weight. 18kg v 11kg. I think it's a no brainer really for an extra £90 new. (unless of course there are other factors at play, like smoothness of tracking etc). Both seem a bit excessive for my humble DSLR, but will be there for the future.

Re cost difference you're comparing Syntrek with Synscan of course - you're probably aware that Syntrek isnt goto? You wont need goto if youre controlling from laptop, but you probably would otherwise. You probably know this but I didnt want you getting a rude surprise. 

[iapa]

I have the

Celestron Advance MQ mount

SLT 10

Skywatcher 80

a 114 somewhere

There's a QHY5 CCD, manual 5 filter wheel, Starsense as well.

On top of that 

• Nikon D90
• Canon 700D
• iPhone with adapter for 1.25" eyepieces.

Lenses for both ranging from 35mm/50mm to 300mm zooms (for both).

Bakhtinov masks for most, as well as for the 130mm OTA

Plan to 

• piggy back the 80mm on the 130
• mount iPhone onto an eye opec for focussing - I could airplay onto a 23" monitor LOL
• I find EQ mounts are a real bar steward for twisting the eyepiece position , serious back breakers.
• piggy back the Nikon or Canon on to the 80mm.

Proposed daytime setup steps.

• put the 130mm onto the AVX and put the horizontal, align with a red light about 4 miles away (damn near horizontal).
• align the spotter to the same point
• align DSLR to the same again

Theory being which ever i look through will have the same object in the centre

Polar scope in the AVX mount, then use the Star Align to refine the alignment.

Kick in the star sense, and I expect I would be pretty damn near polar aligned.

The CCD would go in the 80mm for guiding - I am thinking Starks' app.

After that, Bahtinov mask on the DSL lens

control exposures by software (SofortBild for the Nikon, EOS utility for the Canon)

There is something wrong in there - but I don't know what.....

[Craig20264]

Re cost difference you're comparing Syntrek with Synscan of course - you're probably aware that Syntrek isnt goto? You wont need goto if youre controlling from laptop, but you probably would otherwise. You probably know this but I didnt want you getting a rude surprise. 

And therein lies the beauty of this forum. Always someone willing to share their knowledge. I absolutely wasn't aware of this, so thanks for highlighting it.

Just something else to throw into the cement mixer of equipment decisions that is Astrophotography. 

[Physopto]

One thing about mounts. You will never be satisfied if it under performs to what you want. If you go the extra bit and save up, you hopefully will get the right one first time, not guaranteed of course but hopefully! The EQ6 is an amazing mount for the money. If you can get a good second hand one, brilliant! It will be worth the extra. Buying new is not allways the best way. The savings can be spectacular. If you do decide to sell again in the future the loss is minimal. I had a good EQ6 and was very satisfied with it for several years. Easy to handle and errect. Easy to polar align. Fits in a fairly easily available poly box. So easy to transport. They can be modified fairly cheaply to enhance their abilities. What is not to like.

Can handle a good payload weight, I have seen some way overloaded. Not something I would recommend, but they did it.

Derek

[laser_jock99]

Can handle a good payload weight, I have seen some way overloaded. Not something I would recommend, but they did it.

Derek

The EQ6 can image with double the recomended payload- but it's not for the faint of heart!

[Charic]

With my interest for AP growing, I am keen to get some decent use out of my DSLR................

 Eventually the inevitable question of a scope for imaging will rear its head, and I would ideally like to drop a 200 Reflector on the mount. However, I've read that this mount is probably past it's limit with the weight of the 200. So with this in mind maybe the 150 would be a better option.  

My question is. Is aperture such a big factor with imaging as it is with observing? And maybe i'm barking up the wrong tree with scope choice, or indeed mount choice, and something else, refractor etc would be more suited? I really am in the dark with this, if you'll excuse the pun, so any pointers are gratefully accepted. My copy of "Making Every Photon Count" is on Santas sleigh already i'm told.    

I would rather wait until the budget suits the job, rather than buy and be disappointed.   

I too have a Nikon D5000 system,  and as Phil-lost! #2  mentions, its got the better swivel screen, and I have the accessories to attach the camera to my scope, and so far I have only connected to the scope, and taken a few Moon shots.

I too had lots of questions in the early days and was going to suggest a book, as was suggested to me, but you have already made roads to secure your copy. There are other books available, my wife has bought me one for Christmas? ( shouldn't  leave stuff lying around?) but the one you mention, has the same equipment I use, except for  the smaller aperture? 

It would be my intention to obtain a much smaller aperture than I already own for any future AP work?

[Tinker1947]

I'm thinking next summer to change the 250P-DS i use to a VX6-6 with a 1/10wave mirror thats close to a 10Kg saving on weight this type of scope is something you should consider if its in the budget.....

VX6

http://www.orionoptics.co.uk/VX/vx6-6l.html

250P-DS

http://www.skywatcher.com/product.php?cat=11&id=257