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Old 17-03-2016, 10:47 AM
Chris.B (Christopher)
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Lens or scope???

I am still getting into the astro photography side of things so this may be a silly question.

With shorter focal lengths eg 300-400mm, which has better optics a camera lens or an ED or triplet refractor(or better) and why would you chose one over the other?

I have a 100-400L Canon lens and it is razor sharp for sports.
I can mount that on top the ED100 with uide scope on the HEQ5. Or set up a side by side plate. I was looking at an ED80 but do I need it?

I know good L primes cost as much or more than scopes. Do they produce better shots or not? Vignetting is not as big an issue with camera lenses or is it? They have up to 12 elements to play with and refractors 3 to 6.

Hope you can help clarify it all for me.
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Old 17-03-2016, 11:13 AM
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100-400mm L is quite good.. so you have everything you need for start with AP.
ED100 is also very much OK, especially with field flattener.

Vignetting is sorted out with flats.. so it's not an issue.
Once you gain some experience and "feel" with what you 've got already, you will know how to proceed.
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Old 17-03-2016, 02:56 PM
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I guess a camera lens should have better optics. Why else would camera manufacturers use multiple lens elements if they could produce better quality with a cheaper 2 or 3 lens system?
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Old 17-03-2016, 03:00 PM
Chris.B (Christopher)
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I did think the same thing Geoff, but thought I would ask.
In that case I stick with the 100-400mm
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Old 17-03-2016, 03:12 PM
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I don't agree...

A good apo would have a flatter field and negligible coma. The same can't be said for most camera lenses, regardless of cost. Astrophotographers are IMO more demanding when it comes to image perfection than daytime photographers.
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Old 17-03-2016, 06:43 PM
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So why did I recently purchase a 336mm f4.5 refractor over a 300mm f4.0 camera lens?

Here's a few positives...

- flat field (with flattener) no coma
- built in 10:1 focuser
- came with sturdy dovetail mount, rings & riser blocks.
- no 6 leaf iris star spikes
- handbuilt & tested before shipping
- purpose Built for AP
- fixed aperture

Others may have different opinions, but these made my decision easy.
Hope that's useful
Cheers
Andy
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Old 17-03-2016, 06:59 PM
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I have a 200 f/2.8L (same aperture as the 100-400L fully zoomed in) and has razor sharp images and pinpoint stars to the edge at full aperture. The same applies to my 70-300L at full aperture (fully zoomed in) f/5.6.
Even better than my ED110 + flattener.

A good telephoto lens has a flat field as well as they are designed for photography, and terrestial photography where they are primarily designed for also requires a flat field.

The ED110 is just a good ED scope but it still does have some small color errors, more visible in photos than visually, but OK for me. Visually it is an excellent scope even for planets at high power. Real APO's of 100mm cost at least A$3000, twice the ED110. And the best apo's (Takahashi FSQ-106 or TV NP-101) cost A$6000 or more, almost as much as the Canon 300 f/2.8L, but they are completely color error free and coma free, just like my small telephoto lenses, but with much larger aperture. Moreover they weigh also a lot less: the 300mm f/2.8L weight only 3kg and the 600 f/4L 4kg. No 150mm APO is that lightweight. So if you have the money (A$16000) you have a nice 150mm travel APO.

If you want an 'affordable' 75mm f/4 APO, go for the 300mm f/4L prime, costs about A$1800.
The 100-400L will do the job at 70mm.

Here a review: http://www.dpreview.com/reviews/upgr...mark-ii-review
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Old 17-03-2016, 07:07 PM
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A camera lens has to be able to focus at a range of distances from fairly close to infinity. It also has to be reasonably compact. That requires a complex design and some significant design compromises.

A telescope is designed to focus at infinity. It doesn't need to be as portable. A well designed refractor with a simpler design and high quality optics will beat the crap out of a camera lens for that specific task.

I have seen several examples of long distance terrestrial shots where a good scope is obviously sharper than an expensive lens. If you google a little I'm sure you'll be able to find examples.

That's not to say that you wouldn't be better off with a good camera lens instead of a lower quality scope, of course.

Cheers,
Rick.
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Old 18-03-2016, 10:58 AM
Chris.B (Christopher)
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Horses or courses I guess.

Sad to say my budget will not stretch to a TAK or long 2.8 prime.
I'll keep an eye out for an ED80 and keep plugging away with what I have till then. Will be a while before I catch up to any of the great imagers here or I out grow what I have.

Still was worth bringing it up and see what other think.
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Old 18-03-2016, 12:33 PM
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Can't go far wrong with an ED80, stick a reducer/flattener on it and you'll get down below f/5 easily. The main thing is to get out there and enjoy
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