which would be best for astrophotography?

[HUNTERSBELT]

Hi folks,new some help , having a 8" reflector for a few years and a skywatcher eq5 pro synscan goto , i decided i want to dip into astrophotography , have 2 diffrent telescopes in basket and trying to decide which would be best between svbony 503 102ed  £500- or - skywatcher evostar 100ed ????? £950 with focal reducer

still want to use it for visual use aswell

 

[Budgie1]

Welcome to the SGL and the money pit that is astrophotography.

I started into astrophotography with an EQ5 Pro and Evostar 100ED DS Pro and a Canon DSLR hanging on the end of the scope. It worked, but the scope was a little too big for the mount really and the field of view (FOV) was a little restricted. I still have the scope, but it now resides on the HEQ5 mount and works really well on that.

If I were to do it again then I'd start off with the Evostar 80ED DS Pro. It's smaller, lighter, has wider FOV and is cheaper than the 100ED, but still gives good quality images.

If you want to check the FOV for the different scopes & cameras then try Astronomy Tools to get an idea of what you'll achieve. Also check the second hand market because you can get well kept equipment for about 3/4 of the new price.

[Elp]

What's wrong with the 8 inch reflector?

[michael.h.f.wilkinson]

I think Martin (Budgie1) says makes sense. Going for a slightly shorter focal length makes life a lot easier, I find. My stalwart deep-sky imaging scope I use mainly on my Vixen Great Polaris mount (the EQ5 is a clone of that most cloned mount) is an APM 80 mm F/6 triplet, usually with focal reducer (second-hand Tele-Vue TRF-2008 0.8x reducer/flattener). I only started using longer focal lengths when I got a heavier mount (Great Polaris DX), on which I use  with a scope with similar focal length (but lighter weight) as the SVbony without, and Evostar 100ED with reducer (I use a 6"F/5 Schmidt-Newton).  I also note that while the SVbony scope is faster than the Evostar, it has FPL51 glass, whereas the Evostar FPL53. This would suggest that the colour correction of the Evostar is better (but that isn't guaranteed). Going for a smaller scope like the Evostar 80ED or a triplet like mine can certainly get great results. The forum is littered with examples. Here is one with the APM 80mm at F/4.8 and modded Canon 550D.

 

[Sp@ce_d]

An idea of the sort of targets that interest you would help here advising on the focal length. Generally shorter lengths are recommended for DSO starting out as easier to guide & frame larger nebula. However right now we’re into galaxy season which tends to require a longer focal length. Your 8” reflector may very well be suitable already. A bit more info on what you want to achieve would help narrow down the advice.

[ollypenrice]

I'm afraid I'm tempted to say 'Neither,'  but let's begin with your criteria.  You've gone for 4 inch aperture and this does make sense for visual observing.  Deciding on an aperture, as a first step, though, makes no sense at all for imaging. An experienced imager would think like this:

1) What can my mount support a) in terms of weight and b) in terms of tracking accuracy. Longer focal lengths image at finer image scales and need more accurate tracking. A very good  EQ5 can, under autoguiding, run with a tracking error of about 0.5 arcseconds. You might find it's more like 0.8 or 0.9 arcsecs, though. Whatever it is, you need to multiply that by 2 to find your finest useful image scale. So a guide error of 0.5 arcsecs allows an image scale of 1 arcsec per pixel. An error of 0.8" can image at 1.6 arcsecs per pixel, etc. As a beginner I'd want to be imaging at nothing finer than 2 arcsecs per pixel. Try any scope-camera combination in this calculator to see what it gives. https://www.12dstring.me.uk/fovcalc.php

2) What field of view do I want? Shorter focal length = wider field of view. The calculator above will show you what you'll get in a variety of combinations.

3) How fast do I want the system to be? F ratio is a useful indicator if you're careful or if the camera is already chosen. You can also speed a system up by binning your pixels to make them effectively larger.

The requirement to do visual and imaging with one rig is a bit of a problem since the requirements are not the same. Keeping a Dob for visual and going for an imaging-priorty Apo gets round the issue. If I were starting out in imaging I'd probably go for this: https://www.firstlightoptics.com/william-optics/william-optics-redcat-51-v1-5-apo-f49.html.  Flat field, sharp stars across a large chip, tolerant image scale, fairly fast and good colour correction.

Olly

[Sp@ce_d]

3 hours ago, ollypenrice said:

If I were starting out in imaging I'd probably go for this: https://www.firstlightoptics.com/william-optics/william-optics-redcat-51-v1-5-apo-f49.html.  Flat field, sharp stars across a large chip, tolerant image scale, fairly fast and good colour correction.

Olly

I'd second that.  Having only just returned to imaging after a couple of years or so, out of all my gear this little scope has been a joy to use and reignite my interest. It is so portable, I have it combined with an AM3 mount & ASIair. I can  run outside with it under one arm as a ready to go setup and have it running almost in the same time as it took my ACP controlled Obsy to start up and get going! 😄

Just noticed the OP's post count.. first since 2009! Is that a record?  Congratulations and welcome  🙂

[AstroMuni]

16 hours ago, HUNTERSBELT said:

having a 8" reflector for a few years and a skywatcher eq5 pro synscan goto , i decided i want to dip into astrophotography , have 2 diffrent telescopes in basket and trying to decide which would be best

As queried by @Elp why have you disregarded the 8" reflector? What model do you have? The quickest and possibly the least expensive way to start is attach a camera to the 8" and go from there.

[PhilB61]

What camera are you going to use, with both of the scopes you would need to budget for a field flattener unless using a small sensor. As already mentioned why not try with your current setup, and a DSLR if you have one. You would be under mounted for AP but should be able to get acceptable or even good images if you stack lot's of short exposures, say 15 to 30 sec. It would be a good way of finding out if you enjoy the whole process of data acquisition, calibration and post processing. 

[HUNTERSBELT]

i have a canon 450d and a canon 650d unmodified should i add a clip on filter,probably use other camera piggyback with a f2.8 samyang, i needed something more portable as i live in centre or (center) if your american ,of the city, want to head out into the countryside,i went ahead and bought the svbony 102mm f7 waiting on field flattener coming into stock ,if i need it for them dslr`s ,probably buy a astro-camera in future,all the gear and no idea,thats me ,i know theres probably better scopes i should have picked but typical idiot me ,had money to burn,and can never wait and it seemed to get good reviews on youtube, i guess i think i know what im doing but not so at all, 

joining local astronomy society as i still find polar alignment a pain in the backside

[PhilB61]

Not sure a filter will make much difference with an unmodified camera but others may be able to give a better answer on that. With those DSLR cameras, which have large sensors, a flattener will be required otherwise edge and corner stars will be elongated 

[Elp]

Something like an lextreme does help separate the background sky from emission nebulae rich in ha and o3, even with an unmodified camera. An astro camera (or IR modded dslr) however will have a better pixel response to the photons which pass through.

Edited January 31 by Elp