500mm Mirror lens - Any comments on it's usefulness?

[[1ponders]]

I know these have been mentioned on the site before but I think it was a while ago. So just to refresh my aging memory would someone like to comment on the suitability/usefulness of the 500mm Mirror lens like this one on ebay. (http://cgi.ebay.com.au/500mm-Mirror-Zoom-Lens-for-Canon-20D-30D-300D-350D-400D_W0QQitemZ190148823795QQihZ009Q QcategoryZ30066QQrdZ1QQssPageNameZW D3VQQcmdZViewItem)

Not that I'm really looking to buy one, really, but if the price is right ;) :lol:

[Starkler]

Looks like a miniature sct :lol:

[ballaratdragons]

Paul,

it worries me when no brand name is mentioned.

But this does sound good: 'ALL items will carry a manufacturers warranty which can be serviced in Australia.'

I doubt it would have much light gathering capability though (for astro work). The central obstruction is huge!

[joshman]

it's similar to a prime focus telescope, apparently they give really weird looking bokeh, and in daylight, weird donut shaped light rings and whatnot...

i would do some research on teh wide world of the internets, then make a judgement....

if you do end up getting it, i owuld be most interested to see your results!!!!

btw, it was me who asked a while back ;)

[[1ponders]]

Oh I'm not really serious about it, I'd rather use the ED80, though I'm sure someone sometime will be, which is why I was fairly specific in the thread title.

At f8 (500mm/100mm = f5 so that obstruction is pretty significant) though it might be ok for luna imaging without having to carry a telescope around. Or maybe you could adapt a visual back for it and create a cheap 500mm mak? Just ideas.

[Dennis]

Hi Paul

I have a Tokina 500mm F8 and it produces photos that are a little soft. It really requires the use of a tripod to minimise camera shake. These lenses are quite compact and lightweight; often fooling the unsuspecting photographer into thinking they can hand hold it!

I’ve had mine for over 15 years and only used it on a handful of occasions with average results.

Cheers

Dennis

[[1ponders]]

Do you think the softness is from poor focusing mechanisms, poor mirror or because of the large CO? What's the contrast like with it Dennis? Normally that would be one thing I thought the CO would have caused problems with.

[[1ponders]]

Actually I wonder if a visual back could be fitted to it to take a webcam. Wonder how it would go as a cheap guidescope?

[Dennis]

Hi Paul

I have used the lens on a substantial tripod, using a cable release, at shutter speeds of 1/1000 sec in an attempt to constrain those factors, but the overall image still looks a little soft compared to my normal lenses, or the WO 80mm ED II Apo that I have.

Cheers

Dennis

[Rob_K]

Paul, I've been playing with an MTO 10.5/1100 mirror lens, and probably agree with Dennis that images end up a little soft. I used the lens for all my eclipse shots - lovely scale! My tripod is way too light & ricketty, and anything involving any longer exposure ends up fuzzy (eg totality!). Suspect this is not only movement through the field, but vibration from shutter opening as well. It is the same as shooting through a small scope, but control of focus is much more tricky. In fact you can buy (or make) visual backs to convert the lenses into scopes! Adds a fair bit of weight if you want to piggyback too.

That having been said, it's a lot of fun, with good terrestrial applications too. Anyone got a good heavy tripod? :P

Cheers -

[Dennis]

Hi Paul

Here are a couple of 800 x 600 crops from the 3008 x 2008 jpg original. The 1st image is as is; the 2nd one has been smart sharpened in CS3.

The 3rd file is the original full frame 3008x2008 resampled down to 1024x681. No processing applied.

Subject to lens distance around 10 metres.

Cheers

Dennis

[h0ughy]

you shouldnt show me things like this

[[1ponders]]

:lol: Got Him!!!!!


I knew you'd stick your head in here :lol:

[[1ponders]]

Looks like it could be a fun lens though. :confuse3:

Price is about right, 'eh h0ughy :evil:

What are your thoughts as a guidescope Dennis?

[acropolite]

If it wasn't optically that good, I suspect it would still make a good guidescope with the addition of a mogg adapter.

[acropolite]

BTW Stephan has a 4 inch mak in the icetrade section.

[[1ponders]]

I wonder how these things go for mirror flop? Also notice the rear thread is only 30.5mm, less than 1.25". Wonder that the thread is and how much vignetting would occur?


Dennis? Rob?

I'm really liking the idea of a guidescope. If it worked then $200 for a guidescope wouldn't be too bad, really.

[acropolite]

I'd imagine the focus would be some sort of helical system, go on give it a try, it's only money.....

[[1ponders]]

24.6x18.5 arcmin FOV using a ToUcam/DMK. Not bad, almost full moon width.

[[1ponders]]

Yeah but it's money that could go towards a Tak :lol:


Besides I'd need some clear skies to give it a go. :(

[h0ughy]

well that settles it then doesn't it? I have played with these things before - get a big big hammer and drop it on your foot Paul - take your mind of the shiny bits;):whistle:

[[1ponders]]

Ok, I just had a bit more of a look at the specs and did some calculations. There was an error in my assumptions. The dimensions are 3"x3.5" (Diam x length). ie 75mm wide to outside of lens. That would make the lens aperture only 62.5mm (500/8). But is it really f8 (is an f10 sct really f10 if it doesn't have 200mm clear aperture for a 2000mm scope :shrug: )

[5ash]

it seems alittle light for a decent mirror lens . must be alot of plastic in it.I bought a russian 1000mm f10 maksutov mirror lens earlier in the year and am pleased with the pics it produces.This lens was given a good review in sky and space in 1996. mind you it does weigh sustantially mor than the lens in ebay. have attached an eclipse picture taken through it.
regards philip

[[1ponders]]

4", not that's what I'm talking about. Thanks Philip.

Bet it is a weighty sucker.

[Dennis]

Personally, I'd go for the WO 66mm F6.1 Petzval at $399 with a 10:1 fine focuser. In fact, I did and it is great as a guide scope and a grab and go 'scope too!

Cheers

Dennis

[[1ponders]]

Don't do that Dennis!!! I've been trying not to look at them. How can I afford a FS60-C Tak if I by every little 66 that comes along :P





What's it like for photography? :ashamed:

[h0ughy]

I think Louie took some stunning images with one in the deep sky section

[Dennis]

Hi Paul

I’ve not tried it yet as I lent my SCT to T-mount adapters to Tony (Firstlight) for the Lunar Eclipse, so I haven’t had the opportunity to test it out. I purchased the unit mainly for auto guiding as I had the rings to fit it and it looked a solid ‘scope with the Crayford 10:1 fine focuser, and the best bit - Ron at Sirius Optics (http://www.sirius-optics.com.au/index.htm)had them on special for $359.

I’m a bit wary of Tak ‘scopes these days – they seem to require very expensive, non-standard, custom made adapters in order to do anything with them. It’s okay if you can plot out in advance what you require, but my experience has been that getting the right information is like getting blood out of a stone and then there is a 6 month wait for the adapters.:shrug:

Cheers

Dennis

[[1ponders]]

Yeah that is my concern re the Tak as well. I know this is a bit off topic but I've been humming and hawing over the Petzval since astrofest. I understand that the focuser isn't a "real" 2" focuser and there are some issues getting it to come to focus for photography? Any comments?

$359 :eyepop: that is better than Andrews at $399

[[1ponders]]

Just checked, they've certainly gone up in price now. :doh: I knew I should have gotten it at AF. :doh::doh::doh:

[Dennis]

Hi Paul

Ron had a special purchase offer in the shop at Underwood on a limited number of units he had in stock, before Astrofest. I think the price went up once he sold those particular units and the next order came in?

They do require a 2" SCT diagonal to reach focus though.

Cheers

Dennis

[[1ponders]]

They have an SCT thread on the end and not a T thread :jawdrop::eyepop:

Would they reach focus using a standard SCT to T adapter? (You know the straight one used to attach a SCT FR to a DSLR T ring adapter)

[[1ponders]]

I guess I won't be getting a mirror lens then. ;) Mind you I do like the idea of the compactness of them.

[Dennis]

I've yet to try that, when Tony returns my SCT to T adapters (long & short – hint for Tony).

The SCT ring is shown in the photo below. The Orion Star Shoot Deep Space CCD camera comes to focus using a 1 ¼ diagonal with the focuser racked out around 3cms of the 6cm travel.

Cheers

Dennis

[[1ponders]]

It would be interesting to try with a FR. They normally shorten the distance required to reach focus. Using the Mogg 1.25" reducer requires just over an inch of extra in focus compared to without the adapter and using the extension tube needs something like an extra 2.5 to 3" of infocus. Wonder what that WO 0.8 FR would do :confuse3:

How does it go with the SBIG and filter wheel Dennis? Reacon it will reach focus without the diagonal?

[ving]

i was looking into these cheap 500mm f8 lenses too... theres a kenko one thats f6.3 (i think) which is a bit faster and might be more woth the money than a no-name one. not going down that road now tho.

[[1ponders]]

Where did you see the Kenko one ving?

[ving]

http://cgi.ebay.com.au/New-Kenko-500mm-f-6-3-f6-3-DX-Mirror-Lens-for-Nikon_W0QQitemZ220145540715QQihZ012 QQcategoryZ48556QQrdZ1QQssPageNameZ WD2VQQcmdZViewItem

[[1ponders]]

Cheers, thanks ving. Now can you explain to me why everything costs twice as much in England? Especially seeing as the lens is in Hong Kong :P

[Dennis]

Not tried it yet. I'll try an auto guiding run tonight (weather permitting) with Gerald's STV (on loan) using the WO 66 and let you know.

Cheers

Dennis

[[1ponders]]

:thumbsup:

[Ingo]

Now that's some sexy bokeh! :eyepop:

My guess is that it'll be CA to hell.

[bojan]

Just one small remark from me re mirror (maksutov) lenses..
Anyone who have a guts to do some modification could extend the focus far beyond the original limits, both for FL and position of the focal plane.
I have done this on my MTO1100 (it was an excellent decision to get one ~25 year ago, perfect optics) and then recently on two Rubinar's: 1000mm and 500mm (for my friend, he needed this done for a very special project).
The trick is to remove the stops such that the focus ring can rotate a bit further in both directions.
What you get with this mod is the optical system that can have up to 1/2 of the original FL and the focal plane very close to the lens body, and 2~3x the focal length (and no need for Barlow) and extended focal plane to up to 30cm out.
If you want to know more about it, I can supply you with precise How-to instructions and some photos (for Rubinar 1000, I do not have photos of Rubinar 500 mod but it is very easy to do, much easier that Rubinar 1000 mod)
BTW, The 500 mm lens discussed here by Paul is most likely Rubinar 500 (Russian).
Have a look at www.rugift.com (http://www.rugift.com).