DKD chinese made large refractor lenses on EBAY

[robz (Robert)]

Hi everyone, thought I'd start a second thread on something that may be of interest.

On ebay, there are some large refractors lenses(some with short F ratios, some with medium - longer ratios)for sale by''Telescope Diy''

They don't specify much on optical parameters/specifications, but I was wondering if anyone has heard, good or bad, if these lenses are any good?

They're cheap compared to the big optical companies/brands, but hey, could be a bargain in the making???

http://cgi.ebay.com/D210F3000-refrac...main_0&hash=it

[pmrid (Peter)]

I'd be a bit wary. It's an achromat, not an APO. And it's about f/14 - so it would be better suited to visual lunar/planetary work than astrophotography.
P.

[robz (Robert)]

Thaey also have shorter F ratios on their website/shop.
Probably heaps of C.A., but who knows?

I have emailed them to provide further specs. Let's see if they reply?

[robz (Robert)]

A while back they had a 10 inch Achromat - F5.5!
I have emailed them to see if they still carry it and if they can provide some further specifications.
Lots of Positive feedback there on Ebay................makes you think doesn't it?

[robz (Robert)]

Just for the record, 3 emails to this company have been sent in the past week.
The first address DOES NOT EXIST (apparently), the second email contact details have gone through and not bounced back...................NEITHER HAVE THEY BEEN ANSWERED!!!!!

So,..................me no speeky ingleesh????......or what?

[DavidU (Dave)]

Here is a very detailed report. Looks very good for the money
http://translate.googleusercontent.c...zbog#post43090

[anj026]

You may have heard of this new company that is starting up. They source parts from Asia and Europe and are slowly building a reputation for good customer service and value for money. Their new website is not finished but is due to be ready in November. In the meantime you can communicate via email and order things from them. There has been a lot of discussion on the Cloudy Nights Refractor and Vendor forums.
http://www.istar-optical.com/beta1/index.html

I have been tempted to order a lens myself but already have a few unfinished projects in hand. Maybe later!

[robz (Robert)]

Thanks very much guys!.
Great link/infornation DavidU/anj026!

There's a bit to read and a lot that I don't understand, but generally speaking......it looks o.k?

By the way, I got an email back!....they state that the large 10 inch F1375 is not back in stock yet.

Any other thoughts on the quality or possible downfalls of these lenses?...............is the ASTIGMATISM problem serious?

Will a short F ratio lens like this be any good for High power planetary viewing with Barlows etc?

Cheers,
Rob.

[anj026]

Hi Rob

Large achromats with short focal ratios are not recommended for high power work regardless of whether you use a barlow or not. 4x to 8x per inch of aperture or less will yield the best results. Generally they are best suited for low power wide field of view work such as comet finding or milky way sweeping. There will be significant chromatic abberation (colour fringing) on any bright stars or planets. Their advantage over newtonians for this type of low power work is potentially better contrast and better field illumination (less vignetting of the light cone in wide field use).

Having said that they can be used for limited observation of the moon and planets by stopping down the aperture and effectively increasing the focal ratio. I have a nice 6" f5 refractor that is best at 25x - 45x magnification. I have tried it with a 3" aperture stop to give an f10 ratio and it was very good on the moon and planets up to 100x and great for terrestial observation but I have other scopes for that type of thing.

If you want a large achromat for looking at the moon and planets I would recommend an F ratio or 12 or even better 15 or more.

[robz (Robert)]

Thanks Andy, I think you have answered my thoughts on this and I have decided that I won't go down the Refractor path after a 25 year absence from amateur astronomy.

I think that a SCT and imaging equipment for planetary work may be a better option?

Cheers,
Rob.