32 replies to this topic

[spnc]

The weather gods finally let me have a chance to use the APM 2" AmicI prism. I compared it against an Astro Tech 2" dielectric (99&) diagonal using my APM 152mm f7.9 scope. I had wanted to use my Williams Optics 66mm f6 but that scope has SCT threads on the drawtube and will focus only with a WO 2" diagonal using a SCT nose piece.  The scope doesn't have enough in travel using a SCT to 2" adapter to focus using any 2" diagonal. The TBM 40mm Paragon and 24mm Pan almost come to focus but need just a few more mm of in travel. It doesn't have enough out travel to focus with a 1-1/4 diagonal either. Using a 1-1/4" diagonal, you can hold the eyepiece about an inch out of the diagonal to focus the image with the drawtube racked all the way out. The focuser has 60mm total travel so go figure. Anyway here are my first impressions of the APM diagonal. 

 

Sirius - Yes there is a spike, but it is not too objectionable in my opinion. No added color noted from the APM up to 300x.

Jupiter - The spike is there but fainter and wider than on Sirius. The spike is the width of the planet's disk. Both diagonals showed the same amount of detail at 200x but the sky background appeared darker in the APM. 

Moon - The APM appeared to give an ever so slightly sharper image than the AT diagonal. There was no color along the edge of the disk in the APM at 150x and again the sky background appeared darker. The WO scope will show a trace of purple at higher magnification with a dielectric diagonal as it was marketed as a "semi-apo" at the time, however you want to define that term.

Pleiades - The APM was slightly better than the AT at 30x, darker sky background and sharper stars. Higher magnification wasn't used as I wanted to frame the entire group.

Orion Nebula - Again, I preferred the APM over the AT. Low power, better contrast; high power, slightly sharper stars in the trap at 100x.

 

Overall, I'm happy with the APM for the use I intended, the Moon and deep sky plus terrestrial if I can somehow adapt the WO 66mm to focus using a "normal" 2" diagonal. I need to spend some more time with the APM for further evaluation but my  initial impression is I'm liking it. The dreaded "spike" is only apparent on bright stars and planets. The Moon is so bright that it overwhelms the spike and it isn't seen. I attribute the darker background and shaper image in the APM as the result of less scatter. The APM does require 5-6mm of additional in travel of the focuser versus the AT diagonal.

[TheBigEye]

The weather gods finally let me have a chance to use the APM 2" AmicI prism. I compared it against an Astro Tech 2" dielectric (99&) diagonal using my APM 152mm f7.9 scope. I had wanted to use my Williams Optics 66mm f6 but that scope has SCT threads on the drawtube and will focus only with a WO 2" diagonal using a SCT nose piece.  The scope doesn't have enough in travel using a SCT to 2" adapter to focus using any 2" diagonal. The TBM 40mm Paragon and 24mm Pan almost come to focus but need just a few more mm of in travel. It doesn't have enough out travel to focus with a 1-1/4 diagonal either. Using a 1-1/4" diagonal, you can hold the eyepiece about an inch out of the diagonal to focus the image with the drawtube racked all the way out. The focuser has 60mm total travel so go figure. Anyway here are my first impressions of the APM diagonal. 

 

Sirius - Yes there is a spike, but it is not too objectionable in my opinion. No added color noted from the APM up to 300x.

Jupiter - The spike is there but fainter and wider than on Sirius. The spike is the width of the planet's disk. Both diagonals showed the same amount of detail at 200x but the sky background appeared darker in the APM. 

Moon - The APM appeared to give an ever so slightly sharper image than the AT diagonal. There was no color along the edge of the disk in the APM at 150x and again the sky background appeared darker. The WO scope will show a trace of purple at higher magnification with a dielectric diagonal as it was marketed as a "semi-apo" at the time, however you want to define that term.

Pleiades - The APM was slightly better than the AT at 30x, darker sky background and sharper stars. Higher magnification wasn't used as I wanted to frame the entire group.

Orion Nebula - Again, I preferred the APM over the AT. Low power, better contrast; high power, slightly sharper stars in the trap at 100x.

 

Overall, I'm happy with the APM for the use I intended, the Moon and deep sky plus terrestrial if I can somehow adapt the WO 66mm to focus using a "normal" 2" diagonal. I need to spend some more time with the APM for further evaluation but my  initial impression is I'm liking it. The dreaded "spike" is only apparent on bright stars and planets. The Moon is so bright that it overwhelms the spike and it isn't seen. I attribute the darker background and shaper image in the APM as the result of less scatter. The APM does require 5-6mm of additional in travel of the focuser versus the AT diagonal.

Hi - thanks for posting your interesting review. I have the same opinion regarding the spike in the AMICI - not that big of a deal for the kind of observing I bought the scope for. What I found most interesting was your opinion that the APM AMICI  diagonal (prism) had better contrast and sharper stars than a dielectric mirror type. That's quite a surprise. Perhaps the AstroTech has issues. I had thought about getting a good mirror-based diagonal to do my own comparison. I'll probably do that someday soon. Thanks again for your review!   

[spnc]

I surprised by the difference between the prism and the dielectric also. The difference is subtle but obvious. 

 

I have a two other dielectric diagonals that I also want to compare against the APM prism when time and the weather allow. The WO diagonal and a virgin APM diagonal that came with the 152mm scope and has never been unwrapped. Both are stated as 99% like the AT diagonal and the APM bosts 1/10 lamda on the side of the housing. We shall see.

 

The AT is 9 years old and the WO is 19. That really should not matter. All the eyepieces and diagonals were checked for cleanliness prior to use. Other than blowing the occasional dust particles off, the AT has been cleaned once using liquid and cotton swabs, the WO two, maybe three times. The prism was pristine as would be expected.

[TheBigEye]

I surprised by the difference between the prism and the dielectric also. The difference is subtle but obvious. 

 

I have a two other dielectric diagonals that I also want to compare against the APM prism when time and the weather allow. The WO diagonal and a virgin APM diagonal that came with the 152mm scope and has never been unwrapped. Both are stated as 99% like the AT diagonal and the APM bosts 1/10 lamda on the side of the housing. We shall see.

 

The AT is 9 years old and the WO is 19. That really should not matter. All the eyepieces and diagonals were checked for cleanliness prior to use. Other than blowing the occasional dust particles off, the AT has been cleaned once using liquid and cotton swabs, the WO two, maybe three times. The prism was pristine as would be expected.

Thanks for the additional info. I would be interested to hear your opinion on those comparisons when you get around to it. As a side note, aluminized coatings can degrade over time, but that depends on usage, cleanings, storage conditions, exposure to the elements, quality of the original coating, etc. I'm mostly a big reflector guy and I find that my mirror coatings have significant degradation (pinholes, semi-transparency/loss of reflectivity) issues at 10 to 15 years. Scope is in a dome, protected from the elements, but the temps in the dome vary quite a bit as it is not air-conditioned. YMMV of course, but a 19-year old coating on a mirror diagonal might not be the best yardstick for your evaluation. Either way, I still very interested in hearing back from you on your results. Thanks!       

[The Ardent]

https://www.novac.co...-a-new-century/

[ABQJeff]

The weather gods finally let me have a chance to use the APM 2" AmicI prism. I compared it against an Astro Tech 2" dielectric (99&) diagonal using my APM 152mm f7.9 scope. I had wanted to use my Williams Optics 66mm f6 but that scope has SCT threads on the drawtube and will focus only with a WO 2" diagonal using a SCT nose piece.  The scope doesn't have enough in travel using a SCT to 2" adapter to focus using any 2" diagonal. The TBM 40mm Paragon and 24mm Pan almost come to focus but need just a few more mm of in travel. It doesn't have enough out travel to focus with a 1-1/4 diagonal either. Using a 1-1/4" diagonal, you can hold the eyepiece about an inch out of the diagonal to focus the image with the drawtube racked all the way out. The focuser has 60mm total travel so go figure. Anyway here are my first impressions of the APM diagonal. 

 

Sirius - Yes there is a spike, but it is not too objectionable in my opinion. No added color noted from the APM up to 300x.

Jupiter - The spike is there but fainter and wider than on Sirius. The spike is the width of the planet's disk. Both diagonals showed the same amount of detail at 200x but the sky background appeared darker in the APM. 

Moon - The APM appeared to give an ever so slightly sharper image than the AT diagonal. There was no color along the edge of the disk in the APM at 150x and again the sky background appeared darker. The WO scope will show a trace of purple at higher magnification with a dielectric diagonal as it was marketed as a "semi-apo" at the time, however you want to define that term.

Pleiades - The APM was slightly better than the AT at 30x, darker sky background and sharper stars. Higher magnification wasn't used as I wanted to frame the entire group.

Orion Nebula - Again, I preferred the APM over the AT. Low power, better contrast; high power, slightly sharper stars in the trap at 100x.

 

Overall, I'm happy with the APM for the use I intended, the Moon and deep sky plus terrestrial if I can somehow adapt the WO 66mm to focus using a "normal" 2" diagonal. I need to spend some more time with the APM for further evaluation but my  initial impression is I'm liking it. The dreaded "spike" is only apparent on bright stars and planets. The Moon is so bright that it overwhelms the spike and it isn't seen. I attribute the darker background and shaper image in the APM as the result of less scatter. The APM does require 5-6mm of additional in travel of the focuser versus the AT diagonal.

Note: The APM 2” Amici has SCT threads on its body that the telescope facing nose barrel screws into.

[spnc]

Note: The APM 2” Amici has SCT threads on its body that the telescope facing nose barrel screws into.

I saw your post and thought, yes, finally a solution to adapting the APM prism to the WO scope. Unfortunately it was not to be. The prism diagonal has 50.5 x 1.0mm threads. Standard SCT 2" x 24tpi (50.8 x 0.94mm) won't work. Female SCT adapters have enough slop to screw on to the male threads of the prism nosepiece but male SCT threads will not fit the female threads of the prism body. Makes maybe a half turn before they start to bind up. On to plan C, or D, or E, I've lost count. Might be time for a call to Precise Parts.

 

The APM website does show a mirror 2" diagonal with SCT threads. 

[ABQJeff]

I saw your post and thought, yes, finally a solution to adapting the APM prism to the WO scope. Unfortunately it was not to be. The prism diagonal has 50.5 x 1.0mm threads. Standard SCT 2" x 24tpi (50.8 x 0.94mm) won't work. Female SCT adapters have enough slop to screw on to the male threads of the prism nosepiece but male SCT threads will not fit the female threads of the prism body. Makes maybe a half turn before they start to bind up. On to plan C, or D, or E, I've lost count. Might be time for a call to Precise Parts.

 

The APM website does show a mirror 2" diagonal with SCT threads. 

Must be why my SCT to M48 adapters always get stuck/bound up!