Telescope or just a good zoom lense?

[lnlarxg]

How would you compare astrophotographing with a Telescope or a Camera zoom/prime lens? Whic would you recommend or the pros and cons? 

Reason I ask is, I really would like a nice refractor, but for 400-500pounds I can get a great Canon soon L lens on eBay  (300mm+) which I can use day-to-day 

Also am wondering how to work out the equivalent Camera zoom mm to a telescope? I.e. Is the focal length of a telescope - the zoom mm of the equivalent camera lens?

Thanks a lot!

[happy-kat]

Hi

Camera lenses are often not quite a well corrected and astro work shows the blemishes, I've seen L glass images with poor star shape control at the edges. If you already own the gear then have a go using that but if you don't then take your time work out what you want to image, what suits your mount and see what fits. There's a new 61mm william optics ed apo that's astro designed. Yes the focal length of telescope is equivalent of zoom of camera lens though primes are better, samyang do a corker 135mm f2 that can be used wide open. For the small amount I do I've got some vintage camera lens both have good star shapes though one doesn't handle CA very well. I'm sure you'll get more replies is an interesting question.

[vlaiv]

Lens:

pros: you can use it for daytime / "normal" photography. If it is zoom lens, you can vary focal length / FOV of astro photo.

cons: usually only used for wide field photos, you will be hard pressed to find long focal length one that can't be easily outmatched by a good scope. One should look for lens that is proven as being good for astro photo - good correction when focused at infinity, good objective, small level of aberrations. Possibly mounting problems - lenses are not designed to be mounted on astro mount, and depending on their weight you must take care to get it mounted properly to avoid tilt, shake etc.

Scope pros: many scopes can be used both visually and for photography.

Scope cons: not suited for really wide field shots - most telescopes have FL > 300mm

Yes, zoom lens at a given focal length mm setting is equivalent of telescope with given focal length - just input those in any FOV calculator and you will see how much true field of view it will give you on a target.

[Alien 13]

The big advantage of camera lenses is speed, most quality lenses will operate at f/4 or better with good correction and a large image circle but they have limited back focus so its difficult to use them in mono rigs with filters. The normal max fl for a camera lens is around 400-500 mm but the prices can be eye watering so it makes sense to opt for a telescope at longer focal lengths even if its slower.

If money was no object you would be hard pushed to find any scope at any price that got even close to the specs of something like a Canon 400mm f/2.8L IS II as used in the dragonfly project.

Alan

[Ags]

Dragonfly is very interesting, thanks for the heads-up:

http://www.astro.caltech.edu/~ycao/B&ETalks/vandokkum_bne.pdf

[Gina]

For widefield narrowband imaging Asahi Pentax Super Takumar or SMC Takumar lenses are excellent.  AFAIK all camera lenses designed for terrestrial use are poorly corrected for CA in the red end of the spectrum but with a very narrow bandwidth it's fine - just means Ha/SII focus is slightly different from OIII.  For galaxies (except the enormous Andromeda Nebula) you'll want a telescope anyway for the longer focal length.  For planetary an even longer focal length...

[Gina]

I should add that for anyone starting in imaging, prime lenses are a good choice to get you going.  Or even a DSLR with standard zoom lens as long as you use the manual B setting for long exposures.  Though even shorter exposures can capture The Milky Way from a dark site.  It's not necessary to buy lots of expensive equipment when starting out.

[lnlarxg]

On 30/10/2017 at 11:02, Gina said:

I should add that for anyone starting in imaging, prime lenses are a good choice to get you going.  Or even a DSLR with standard zoom lens as long as you use the manual B setting for long exposures.  Though even shorter exposures can capture The Milky Way from a dark site.  It's not necessary to buy lots of expensive equipment when starting out.

Good advise all, I am definitely going cheap first and get good at it until I get upgraded to great equipments

i was just debating on a good Canon L, but massively inspired by the thread "Imaaging with 130pds" I am. Ow waiting for my 130pds delivery. Keeping my Sw200p dob for visual

[Gina]

I gather the 130pds is a good starter scope   But you will want a tracking mount except for bright objects.  The moon is a good object to start on - very bright.  DON'T consider the sun without a special filter - it will melt things!  And never look at the sun, particularly with telescope or binoculars it will BLIND you.  You may be well aware of this but it's a worthwhile warning for anyone starting in astronomy. 

I thoroughly recommend buying the book "Making Every Photon Count" by Steve Richards (steppenwolf on here).  Available from FLO.  Best £20 I've ever spent!