Canon prime "L" lens VS ED refractor

[stan26]

Hi folks, Would like to know you experience/opinions with this one. It looks like in the near future I may find myself in the fortunate position to upgrade my scope (currently an ST102 achro). I would like a canon L to improve my aviation photography but would also like an APO scope for my astro photography, but would not be able to afford/justify both, SO how do you think something like a canon 400mm F5.6 L prime lens would do at astrophotography...? how would it compare to your average ED scope.......Two birds with one stone I'm thinking..........

Any advice appreciated

Cheers

Stan:)

[MG1]

I'll leave a more scientific response to someone with a little more know-how, but I would have thought that you want as few elements as possible in the optical path. Therefore higher transmittance of light to your sensor.

[angusb1]

If you are planning to use it with your 500D with its DIGIC 4 processor it could be a pretty good tool. It's fairly fast and the optics are of an excellent quality. With something like APT you will be able to stop it down (although it should be very sharp wide open and also sharp right to the edge of the field even when wide open). You can also make extremely fine adjustments to focus from a PC while using FWHM measurements or a focusing mask so you can get your focus spot on. If you're autoguiding you may well have a PC on hand anyway so you can take advantage of a tool like APT to control your exposure times and focusing. It should also be quite well weather sealed which is an advantage when you're using it in dewy conditions. I think this lens has a fairly flat field as well.

If you ever plan to move to a CCD you would lose most of these advantages, you would need an adaptor costing £130 to mount the camera to the lens, and you would need to find some way of focusing (there is a telescope service focusing tool for £55). If you decided you wanted a modified DSLR to get more Ha you would need to go for another DIGIC4 based camera to retain the remote focusing advantage.

Your alternative for similar money would be something like an 80mm 480mm focal length triplet with a field flattener. You would gain 10% aperture and the ability to use it visually or with a CCD in future. It is also easier to mount a finder to a scope as it has rings whereas with a tele lens you would have to bodge something onto the hotshoe or use a side by side bar with something like an ST80 and finder, but then you could use this for guiding too. You would lose the ability to autofocus and a very small amount of speed.

HTH

[themos]

an 80mm 480mm focal length triplet with a field flattener.

A Meade 5000 triplet 80/480 was bought secondhand for £280. Throw in another £70 or so for a SW f/6 flattener and you'd need 3 times that cash for the new Canon.

[angusb1]

A Meade 5000 triplet 80/480 was bought secondhand for £280. Throw in another £70 or so for a SW f/6 flattener and you'd need 3 times that cash for the new Canon.

I was trying to compare apples with apples. A new canon 400/5.6 is about £1000. You could buy a TS 80/480 FPL53 triplet for about the same money.

The OP didn't say whether he was buying new or not so I was comparing on the basis of a similar scope in terms of design and cost new.

It's not fair to say that an APO will always be cheaper than a tele lens, you can easily spend the same money new if you buy a really expensive APO.

[themos]

Quite correct. But it's probably easier to source a secondhand triplet than a secondhand L lens. Having said that, I just found a lot of used 70-300 non-L f/5.6 for just under £300.

[Psychobilly]

I'm moving from Scopes to Lenses - Simply becasue the camera lenses are getting far more use... I wouldnt't have fancied shooting the rally cars with the Vixen,WO oR TV scopes I have...

I like shooting widefield with DSLR's instead of mosaics with scopes (been there done that and because of the "British weather" I was ending up with too many unfinished projects......

You can get flare artefacts with very bright starts in the FOV with the lenses

The initial trials with 100-400 f4.5-5.6L IS USM I recently bought look interesting...

I haven't bought an L prime (yet) but have 24-105 f4L IS USM, 70-200 f4L , and the 100-400 f4.5-5.6L IS USM. The 70-200 is surplus and may move on..

Peter...