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APM 152 ED APO club

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#651 NCC-2893

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Posted 18 November 2020 - 04:11 PM

Part 2

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#652 NCC-2893

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Posted 18 November 2020 - 04:22 PM

Part 3

 

Quality of the finder is pretty good but actually not easy to compare with a 50mm finder in terms of aperture. I like the small Skywatcher finder, too. But it is nothing wrong to go with a 80mm with such a large refractor. Good thing is you can change the eyepiece. 

 

I also bought the APM 24mm 55° (?) cross hair eypeace which I cannot really recommend. It has at least a cross hair laugh.gif but quite strong distortion on the edge. 

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#653 CHASLX200

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Posted 18 November 2020 - 07:06 PM

I used a ST-80 as a finder and helped with back weight on my 152.


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#654 ASTERON

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Posted 19 November 2020 - 08:20 AM

I use a Sky-Watcher 6x30 RACI amici finder on my APM 152. It's a small finder, but it has a wide field of view and that makes it easy to get recognizable stars in the field that can also be seen with the naked eye. I generally can't see fainter deep-sky objects in it, but I can see enough stars to easily put the crosshairs over the position of the object, much like you do with a Telrad or red dot finder with the naked eye, I just have 6x higher precision and can see many more stars, making starhopping very easy. I actually prefer starhopping with the wee 6x30 finder over my 10x60 RACI for this reason, especially in summer, where my nights are very bright and I have trouble seeing enough naked eye stars to use a bigger finderscope, without making the starhops extremely long. 

 

I'm thinking about building a small super-high-end RACI finder from an ASKAR FMA 180, a Baader T2 Amici diagonal and a 24mm ES68 eyepiece. 7.5x magnification and 9° TFOV, with 40mm aperture. 

 

 

Clear skies!

Thomas, Denmark

Hi Thomas,

thanks for your reply.   I realize your opinion about 6X30 RACI finder for Star hopping.  My setup will be using  a Push- to on a DM6+ encoders with a Nexus +Sky Safari on an android tablet, so probably no star hopping with this Combo.  The reason I want a good finder is that I want high precision in alignment but I would like to be able to change the finder eyepiece for various reasons.  The interchangeable eyepiece will be good for dual use of the finder as a small RFT while changing to cross-hair illuminated eyepiece for alignment work.  and also gives freedom to change magnification and TFOV.

I like your  Idea of constructing a "super finder" from  different partsbow.gif bow.gif , It sounds very nice with the only caviat that you will have to sell a kidney to finance the parts. lol.gif

 

If you ever get this finder, don't forget to post pictures, !


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#655 ASTERON

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Posted 19 November 2020 - 08:25 AM

Part1

APM ED APO 152mm with APM finder 80mm. 

Here are at least some pictures, rest to follow. 

NCC 2893,

Wow, that is a large beast of a finder (may serve right to balance the scope though).

Thanks for the pictures which nicely demonstrate the relative sizes of the scope vs. finder.

Lihu



#656 ASTERON

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Posted 19 November 2020 - 08:32 AM

Part 3

 

Quality of the finder is pretty good but actually not easy to compare with a 50mm finder in terms of aperture. I like the small Skywatcher finder, too. But it is nothing wrong to go with a 80mm with such a large refractor. Good thing is you can change the eyepiece. 

 

I also bought the APM 24mm 55° (?) cross hair eypeace which I cannot really recommend. It has at least a cross hair laugh.gif but quite strong distortion on the edge. 

Yes, I really need to be able to change the eyepiece. I wonder how good will it be as a guide-scope being an Achromat ?

Thanks for the warning about the APM eyepiece waytogo.gif , I will provbably be using a Televue plossel or a Nagler  or an ES 68 degree (which I already have, so I don't need to buy specially for the finder) on the finder. 


Edited by ASTERON, 19 November 2020 - 08:33 AM.


#657 ASTERON

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Posted 19 November 2020 - 08:41 AM

I used a ST-80 as a finder and helped with back weight on my 152.

Hi CHASLX200,

I also have an Orion ST80, which I may use as a finder, I will have to get an Amichi Prism diagonal for it's 1,25" drawtube and I will have to find tube rings to mount it  properly but since it's a 400mm focal length it may not be bad for  a variable magnification finder by changing eyepieces.

The end of the eyepiece holder of the Orion ST-80 is threaded on the outside.  Do you know if it is a male T or T2 thread ? if so It will be easy to correct the Baader Amichi prism to it directly.


Edited by ASTERON, 19 November 2020 - 08:52 AM.


#658 NCC-2893

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Posted 19 November 2020 - 04:02 PM

And now something totally diffrent:

 

I really like the hardcase which comes with the frac but I think it needs a handle in the middle enabling you to carry it like a suitcase.

 

This is not a beauty version, but it works. Actually you could use the same handles like on the case but it was not awailable in the shop. And I needed a quick solution. Please see picturs.

 

Edit: And it is perfectly balanced when carrying. 

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Edited by NCC-2893, 19 November 2020 - 05:54 PM.


#659 NCC-2893

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Posted 19 November 2020 - 04:03 PM

More pix

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#660 NCC-2893

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Posted 19 November 2020 - 04:05 PM

Sorry for the bad picture quality... 

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#661 CHASLX200

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Posted 19 November 2020 - 07:05 PM

Hi CHASLX200,

I also have an Orion ST80, which I may use as a finder, I will have to get an Amichi Prism diagonal for it's 1,25" drawtube and I will have to find tube rings to mount it  properly but since it's a 400mm focal length it may not be bad for  a variable magnification finder by changing eyepieces.

The end of the eyepiece holder of the Orion ST-80 is threaded on the outside.  Do you know if it is a male T or T2 thread ? if so It will be easy to correct the Baader Amichi prism to it directly.

I would have no clue as i don't have the scopes anymore.



#662 tom_fowler

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Posted 21 November 2020 - 12:07 PM

I have a 152mm ED, and like it very much.  I recently purchased one of Markus' 115mm f/7 triplet LZOS scopes, which is a splendid piece of equipment.  I am curious if anyone in this august group has compared the 152mm ED to the 152mm LZOS that Markus sells?  At 3x the price, what is the difference?  Based on the 115mm I am thinking of upgrading, but the upgrade cost is pretty steep, especially if there is only a minor improvement.  I've attached an image of M13 taken with the 152mm a few years back.M13 reduced.jpg


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#663 spazmore

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Posted 23 November 2020 - 11:25 PM

Reducers for maximum FOV on the APM 152ED - 

 

I have the Explore Scientific 0.7x reducer/flattener, and it "works", but has some visible vignetting on my APS-C sensor, and pixel-peeping reveals a small amount of CA visible on some stars. Has anyone directly compared the the ES 0.7x to the Starizona APEX-L 0.65x? I have an Altair Lightwave 0.6x FF/FR, but it's really meant for smaller sensors.

 

A pic taken with the APM and the 0.7x ES, adjusted to better show vignetting:

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Edited by aa5te, 23 November 2020 - 11:27 PM.


#664 spazmore

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Posted 23 November 2020 - 11:26 PM

Close up to show CA mentioned above:

 

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#665 StarAlert

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Posted 23 November 2020 - 11:43 PM

It's my understanding that a blue fringe on one side and a red fringe on the other is atmospheric dispersion, not CA. I am no expert, though. 

 

Close up to show CA mentioned above:


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#666 spazmore

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Posted 23 November 2020 - 11:46 PM

It's my understanding that a blue fringe on one side and a red fringe on the other is atmospheric dispersion, not CA. I am no expert, though. 

You may be right. I read that too, and I wondered that. What leads me to believe otherwise is that this is exactly like the constant color fringing that I, and others, have observed with the Orion 110mm Eon/iOptron 108mm Versa f/6 ED doublets.



#667 Astrojensen

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Posted 24 November 2020 - 10:51 AM

It's my understanding that a blue fringe on one side and a red fringe on the other is atmospheric dispersion, not CA. I am no expert, though. 

 

You may be right. I read that too, and I wondered that. What leads me to believe otherwise is that this is exactly like the constant color fringing that I, and others, have observed with the Orion 110mm Eon/iOptron 108mm Versa f/6 ED doublets.

 

You may be right. I read that too, and I wondered that. What leads me to believe otherwise is that this is exactly like the constant color fringing that I, and others, have observed with the Orion 110mm Eon/iOptron 108mm Versa f/6 ED doublets.

If constant and always on the same side/same orientation, then it can be a sign of very slight misalignment in the doublet ED objective. I've seen this in my own 72mm William Optics ED doublet. 

 

 

Clear skies!

Thomas, Denmark


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#668 BillP

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Posted 24 November 2020 - 11:54 AM

Close up to show CA mentioned above:

I would imagine, in an imaging train, there could be multiple reasons.  I suggest you post this in the imaging forum and let that group go thru all the different possibilities with you.  Might behoove you to image an artificial star indoors too to eliminate atmospheric effects.


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#669 Heywood

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Posted 24 November 2020 - 01:00 PM

If constant and always on the same side/same orientation, then it can be a sign of very slight misalignment in the doublet ED objective. I've seen this in my own 72mm William Optics ED doublet.


Clear skies!
Thomas, Denmark


I'm betting it's a slight misalignment, as Thomas stated.

#670 tom_fowler

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Posted 13 December 2020 - 07:41 PM

Regarding the Lunt/APM 152mm ED and triplet refractors like the TEC 140mm, I received some info from a fellow in the TEC group, who has both the Lunt 152mm and a TEC 140ED, which is a triplet.  He told me that he did a comparison, and said (not surprisingly) that the TEC 140 was sharper, but more to the point, he said that he tried stopping down the 152mm to 140mm and then to 130mm.  He said that this noticeably improved its performance, especially at 130mm, though color correction was not equal to the TEC.  I had my doubts so I tried it myself.  I made a mask to stop the Lunt down to 142mm, i.e., a reduction of 10mm.  I used distant trees as a target, looking for details in the bark during daylight.  Somewhat to my surprise, there was a noticeable improvement in sharpness.  I compared the full aperture and the stopped down scope using a Baader binoviewer, and Televue Delite eyepieces at 7mm, 5mm, and 4mm, giving 214X, 300X, and 375X.  I also tried a Baader 6mm ortho, giving 250X.  In every case there was a noticeable improvement in sharpness, and a reduction in purple fringing.  I'm not sure that any more detail was visible at 375X than at 300X, but the image still looked quite sharp even at that power, greater than 50X/inch.  The full-aperture images were also good, just not as good.  I did recently recollimate my Lunt 152mm with the (overpriced) Takahashi collimating scope, so I think it is in optimal condition, with reported Strehl of 0.94.  At the next opportunity, I'll do this test on the moon.  Meanwhile if you want to try it yourself, I can send you the PowerPoint slide that I used to print my 142mm mask.  Just print the slide on the heaviest stock that you have, cut it out, and in insert it into the dew shield just in front of the lens housing.  Contact me at tfowler@gmu.edu.  I did the printing on an HP 8610 inkjet printer, but in theory any printer should print the mask image to the right scale.  Check with a ruler, however.  Assuming that this is correct, obviously a $3K ED scope won't match a $9K 152mm triplet, or even a $7.5K 140mm triplet.  But stopping down by 10mm does close the gap enough that it becomes harder to justify $7.5K or $9K for a new scope.  I would not personally accept stopping the scope down to 130mm; at that point I would just opt for a 130mm triplet, which is smaller and lighter. 


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#671 Deadlake

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Posted 14 December 2020 - 05:30 AM

Part 3

 

Quality of the finder is pretty good but actually not easy to compare with a 50mm finder in terms of aperture. I like the small Skywatcher finder, too. But it is nothing wrong to go with a 80mm with such a large refractor. Good thing is you can change the eyepiece. 

 

I also bought the APM 24mm 55° (?) cross hair eypeace which I cannot really recommend. It has at least a cross hair laugh.gif but quite strong distortion on the edge. 

The APM eyepiece is not working for me either. However this could be good,

https://www.baader-p...iding-eyepiece/

Another advantage is the light is built in and not a huge torch stuck on the side. smile.gif



#672 drd715

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Posted 14 December 2020 - 07:44 AM

Regarding the Lunt/APM 152mm ED and triplet refractors like the TEC 140mm, I received some info from a fellow in the TEC group, who has both the Lunt 152mm and a TEC 140ED, which is a triplet.  He told me that he did a comparison, and said (not surprisingly) that the TEC 140 was sharper, but more to the point, he said that he tried stopping down the 152mm to 140mm and then to 130mm.  He said that this noticeably improved its performance, especially at 130mm, though color correction was not equal to the TEC.  I had my doubts so I tried it myself.  I made a mask to stop the Lunt down to 142mm, i.e., a reduction of 10mm.  I used distant trees as a target, looking for details in the bark during daylight.  Somewhat to my surprise, there was a noticeable improvement in sharpness.  I compared the full aperture and the stopped down scope using a Baader binoviewer, and Televue Delite eyepieces at 7mm, 5mm, and 4mm, giving 214X, 300X, and 375X.  I also tried a Baader 6mm ortho, giving 250X.  In every case there was a noticeable improvement in sharpness, and a reduction in purple fringing.  I'm not sure that any more detail was visible at 375X than at 300X, but the image still looked quite sharp even at that power, greater than 50X/inch.  The full-aperture images were also good, just not as good.  I did recently recollimate my Lunt 152mm with the (overpriced) Takahashi collimating scope, so I think it is in optimal condition, with reported Strehl of 0.94.  At the next opportunity, I'll do this test on the moon.  Meanwhile if you want to try it yourself, I can send you the PowerPoint slide that I used to print my 142mm mask.  Just print the slide on the heaviest stock that you have, cut it out, and in insert it into the dew shield just in front of the lens housing.  Contact me at tfowler@gmu.edu.  I did the printing on an HP 8610 inkjet printer, but in theory any printer should print the mask image to the right scale.  Check with a ruler, however.  Assuming that this is correct, obviously a $3K ED scope won't match a $9K 152mm triplet, or even a $7.5K 140mm triplet.  But stopping down by 10mm does close the gap enough that it becomes harder to justify $7.5K or $9K for a new scope.  I would not personally accept stopping the scope down to 130mm; at that point I would just opt for a 130mm triplet, which is smaller and lighter. 

It's not uncommon to find edge deficiencies (turned edge) in mass produced lenses. Masking the outer 10mm can clean up the image in this case. Also the slight rise in F number may contribute to less CA. 


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#673 tom_fowler

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Posted 14 December 2020 - 08:46 AM

Yes the edge deficiencies show up in the test report that came with the lens.  This is common in mirrors as well as lenses.  I suspect that masking the edge also improved the Strehl, though I have no way of measuring that. But if the RMS is reduced to 0.03 from 0.039, that would make the Strehl about 0.96.  Not unreasonable looking at the test report, which shows that most of the deviation does indeed come at the very edges.

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#674 daquad

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Posted 14 December 2020 - 09:56 AM

Regarding the Lunt/APM 152mm ED and triplet refractors like the TEC 140mm, I received some info from a fellow in the TEC group, who has both the Lunt 152mm and a TEC 140ED, which is a triplet.  He told me that he did a comparison, and said (not surprisingly) that the TEC 140 was sharper, but more to the point, he said that he tried stopping down the 152mm to 140mm and then to 130mm.  He said that this noticeably improved its performance, especially at 130mm, though color correction was not equal to the TEC.  I had my doubts so I tried it myself.  I made a mask to stop the Lunt down to 142mm, i.e., a reduction of 10mm.  I used distant trees as a target, looking for details in the bark during daylight.  Somewhat to my surprise, there was a noticeable improvement in sharpness.  I compared the full aperture and the stopped down scope using a Baader binoviewer, and Televue Delite eyepieces at 7mm, 5mm, and 4mm, giving 214X, 300X, and 375X.  I also tried a Baader 6mm ortho, giving 250X.  In every case there was a noticeable improvement in sharpness, and a reduction in purple fringing.  I'm not sure that any more detail was visible at 375X than at 300X, but the image still looked quite sharp even at that power, greater than 50X/inch.  The full-aperture images were also good, just not as good.  I did recently recollimate my Lunt 152mm with the (overpriced) Takahashi collimating scope, so I think it is in optimal condition, with reported Strehl of 0.94.  At the next opportunity, I'll do this test on the moon.  Meanwhile if you want to try it yourself, I can send you the PowerPoint slide that I used to print my 142mm mask.  Just print the slide on the heaviest stock that you have, cut it out, and in insert it into the dew shield just in front of the lens housing.  Contact me at tfowler@gmu.edu.  I did the printing on an HP 8610 inkjet printer, but in theory any printer should print the mask image to the right scale.  Check with a ruler, however.  Assuming that this is correct, obviously a $3K ED scope won't match a $9K 152mm triplet, or even a $7.5K 140mm triplet.  But stopping down by 10mm does close the gap enough that it becomes harder to justify $7.5K or $9K for a new scope.  I would not personally accept stopping the scope down to 130mm; at that point I would just opt for a 130mm triplet, which is smaller and lighter. 

Good test and useful conclusion.  In addition the 152 APM should perform a little better at lower powers on deep sky.

 

Dom Q.



#675 Mitrovarr

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Posted 14 December 2020 - 11:49 AM

I would imagine, in an imaging train, there could be multiple reasons.  I suggest you post this in the imaging forum and let that group go thru all the different possibilities with you.  Might behoove you to image an artificial star indoors too to eliminate atmospheric effects.

Easy way to check, rotate the telescope 180 degrees but not the rest of the imaging train. If it's the telescope, the distortion will rotate with the telescope.




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