APM 2 inch Erect-Image-prism with fast-lock

[Doc]

Father Christmas was very nice to me and bought me an APM 2 inch Erect-Image-prism with fast-lock.

 

http://www.apm-telescopes.de/en/optical-accessories/stardiagonal-mirror--prism/apm-2-inch-erect-image-prism-fast-lock-ultra-broadband-coating

 

According to the product information on the website the diagonal has a full 46mm of free aperture, the most ever developed. 

 

Well tonight is meant to be a clear night so fingers crossed I can give a test and of course I will let you know what it is like. But in the meanwhile I can say thet it arrived in a very nice sturdy white box, which was padded with styrofoam type of material. The diagonal itself feels very well made and oozes quality. It feels weighty and the click lock system works very well indeed. 

 

While setting up today I compared both my Skywatcher and APM on a distant ariel and I can confirm that the APM diagonal needs 11mm of in travel of the focuser to come to the same point that the Skywatcher focused.

 

Anyway here's a few photo's to wet your appertite.

 

 

 

 

 

 

 

 

 

[Smithysteve]

Very nice, obviously just what you wanted from Santa - presumably you sent him a wish list? ??

[Tweedledee]

That looks very nice. I'm surprised it didn't need more in travel than 11mm! 

[Doc]

I was surprised as well Pete but I used the graduated scale on the focuser and it went from 77mm for the non prism diagonal to 66mm for the APM prism diagonal.

 

I had a 3 1/2 hour session tonight and it took a little while to get used to it but I must say I'm pretty impressed. On the moon it was fantastic, in my opinion it didn't degrade in any way. I got out my Rukl moon atlas and I followed certain areas of the moons surface and it was so easy to follow as everything is the correct way up. 

 

Star hopping was also dead easy, I used Skysafari and found a lot of dim objects such as the Eskimo Nebula with ease. I can't believe how much easier star hopping is without the need to think which way I need to go, left is left and right is right, simples. I managed to find Uranus by star hopping so I'm pretty impressed.

 

Star colours seem a lot more vivid using the APM Prism diagonal instead of my Skywatcher diagonal. Yellow and red stars really seemed to pop with colour.

 

I inserted my 2" eyepieces into the both focusers and compared the view and I couldn't detect any restrictions or light loss so I cannot see any reason not to believe that the prism diagonal has less then the 46mm aperture it claimns to have.

 

There was two negatives the first one was on certain stars like Capella and Procyon I could easily detect a line similar to what a spider vane produces. I've read about this line before and it is produced by the joint in the prism. APM says it is almost invisible and on medium to dim stars I will agree but on bright stars it's quite easy to see. The second negative was brighter stars seemed to be a little bloated compared to the normal diagonal, this was very slight and didn't occur at all on dimmer stars. I'm not sure why this happened, it needs a little detective work to find out if indeed it was the prism or atmospheric conditions.

 

None of the above observations are completely scientific and I would imagine there are better tests to do, but I don't know them. Overall I'm happy with the prism diagonal especially on Lunar work it was simply fantastic.

[tuckstar]

Nice write up Mick. I have been looking at the baader zeiss prism for my zeiss, but the smaller one, the 2 inch is out of my price range and don't think I would gain much with the 2 inch on such a narrow scope. Interesting to see how much that line shows.

Edited December 28, 2017 by tuckstar

[+Ibbo]

I got the non erecting one and tried for an hour or so and was impressed with the views over my old Revalation mirrored diagonal as the better one has a new job to do (Phil noticed last night).

 

I did not notice the line Mick but I was a bit cramped for room and direction in the obs and a better trial run will be in the open when we get a night.

Tried Castor,Pollux and Betlegeuse then a quick run round the clusters of Auriga before the clouds came over, oh and the Eskimno in Gem

[Werisit]

Thank you for that Mick. I've been looking for a quality one of these for quite a while now. I bought a Baader one but I'm sure it was faulty as the image wasn't sharp at any point. I don't speak German so I couldn't make the supplier understand that it wasn't a problem of lack of focus travel. I got them to swap it for a Baader BBHS (Silver mirror T2 Diagonal). So I ordered the APM and it arrived on Monday. I gave it a short test that night on the ST120 but I've been laid low with a cold so missed a few clear night opportunities. Initial impression was that it was crisp, and bright. I'm really looking forward to doing some wide field scanning with it. Might even have to buy some decent 2" EP's.

One note is that I could only just achieve focus on the ST 120. I'll do some minor mods and try to gain another 3mm or so of in travel. I don't think there will be a problem with the EDT 130.

There is an interesting review on different types of star diagonal here.

 

 http://www.baader-planetarium.de/news/mirror-Prism-Dielectric-Diagonal-Comparison_2014-03-06_v2.pdf

[Doc]

Had another session tonight and I will confirm the APM gives brighter views then a normal Skywatcher diagonal. The only niggly problem but you do forget about it after a while is the line that appears on brighter stars. But the best thing off all is how easy it is to star hop due to the correct view you get, this is awesome and a big benifit.

 

Thanks for the link Alan I will have a look later.