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

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




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.


















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

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

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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.

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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 by tuckstar

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