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Which Apochromat for DSO imaging on an AVX?

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#26 luter68

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Posted 10 September 2018 - 01:31 AM

The mount behaviour is not only a question of weight but inertia. If you get two counter weights and put them as far up as possible instead of one at the end of the bar the over all weight is more while the inertia (the force that stands against

accellerating a rotation) is lower as it goes by the distance squared. It is the same thing as the ice skater doing a pirouette by pulling the arms close to the body. The less inertia the better the mount can do a correction, which is in fact a change of speed. All premium mount manuals tell you to do so.I fully agree.

That's right. However, that would be part of the test. In fact, by adding weight, I will have to move out the CW. Reducing momentum is also one reason why I was thinking of an OAG instead of a guide scope mounted on top of the imaging one. Although more cumbersome to use, it adds less weight and, in particular, momentum. In any case, making a table with the weight budget may be useful anyway.



#27 the Elf

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Posted 10 September 2018 - 03:36 AM

I'm using the OAG with my RC because a slight tilt of the primary mirror makes the image move while the mount rotates the scope. There is no other option for this scope. With the refractor I use it as well and it is easier there, because the refractor came with a manual rotator. You don't need to loosen the camera to rotate and don't loose focus. Only if there is no guidstar or the orientation of the image does not allow access to the guide star I put the guide scope on it. The difference in weight is quite large. OAG reduces the risk of differential flex. One day I found my guide scopes front lens loose. That was fun! If you can handle OAG, do it!

Speaking about weight a scope with a field corrector inside is probably less weight than an external flattener. Plus you don't have to deal with the flattener to sensor spacing. A con is the short backfocus: many imaging scopes cannot be operated with a diagonal or need a very short special one. If you don't observe that's not relevant for you.

Another major point is a carbon tube. It extends less with temperature and the need to correct focus while the ambient temperature changes becomes less. If you want to add automatic motorized focus this is not a point. If weight is your main concern (and I agree it should be!) carbon saves weight and you can image without automatic focus more convenient, so double weight save. There is one 80mm carbon refractor available, but I don't remember the brand. You will find it..


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#28 luter68

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Posted 10 September 2018 - 06:34 AM

I'm using the OAG with my RC because a slight tilt of the primary mirror makes the image move while the mount rotates the scope. There is no other option for this scope. With the refractor I use it as well and it is easier there, because the refractor came with a manual rotator. You don't need to loosen the camera to rotate and don't loose focus. Only if there is no guidstar or the orientation of the image does not allow access to the guide star I put the guide scope on it. The difference in weight is quite large. OAG reduces the risk of differential flex. One day I found my guide scopes front lens loose. That was fun! If you can handle OAG, do it!

Speaking about weight a scope with a field corrector inside is probably less weight than an external flattener. Plus you don't have to deal with the flattener to sensor spacing. A con is the short backfocus: many imaging scopes cannot be operated with a diagonal or need a very short special one. If you don't observe that's not relevant for you.

Another major point is a carbon tube. It extends less with temperature and the need to correct focus while the ambient temperature changes becomes less. If you want to add automatic motorized focus this is not a point. If weight is your main concern (and I agree it should be!) carbon saves weight and you can image without automatic focus more convenient, so double weight save. There is one 80mm carbon refractor available, but I don't remember the brand. You will find it..

Thanks, very precious comments!

About the carbon tube, once I think I read that aluminum may actually be preferable for temperature induced focus shift as the changing on the length of the tube sort of correct the deformation of the triplet. In fact, I was considering an aluminum tube up to now. I will check it up again.



#29 bobzeq25

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Posted 10 September 2018 - 10:21 AM

Thanks, very precious comments!

About the carbon tube, once I think I read that aluminum may actually be preferable for temperature induced focus shift as the changing on the length of the tube sort of correct the deformation of the triplet. In fact, I was considering an aluminum tube up to now. I will check it up again.

It's a complicated design issue.  The best thing is when the designer matches the lens cell to the tube.  As always, you get what you pay for.


Edited by bobzeq25, 10 September 2018 - 10:22 AM.

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#30 RogeZ

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Posted 10 September 2018 - 10:45 AM

I would seriosly consider the Meade 70Q and other flavors. You dont want too fast of scope either with a small budget as a good solid fast scope is not cheap.

I should also recommend the new 8” RASA which should be a killer scope for that setup. Regardless of scope you can always bin 2x2 and help the mount.
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#31 luter68

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Posted 11 September 2018 - 01:21 AM

I would seriosly consider the Meade 70Q and other flavors. You dont want too fast of scope either with a small budget as a good solid fast scope is not cheap.

I should also recommend the new 8” RASA which should be a killer scope for that setup. Regardless of scope you can always bin 2x2 and help the mount.

I didn't know about the upcoming RASA 8".... Indeed, it looks amazing and at a seemingly affordable price. However, I think that with its very fast aperture and just 29mm back focus,  it is much better suited for OSC cameras. I have now gone on the NB route and I really like it. Well, a slightly slower version with 20-30 mm more back focus would have been ideal.

 

About the 70mm f/5 quadruplets, does anyone knows whether a reducer for flat field scopes such as the TeleVue 0.8x NPR1073

https://www.teleskop...field-Apos.html

could be used with those?

The nice thing about the esprit 80 is that it seems to work with a flattener/reducer, bringing it down to f/4 that would be rather nice for NB.



#32 the Elf

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Posted 11 September 2018 - 02:49 AM

TS states it can. Tele Vue made it for their Petzval types. A Petzval has got a group of lenses relatively far away from the front group, so there is some similarity in the design. There is an article by Baader Planetarium, only available in German where they tested the NPR1073 at the PlaneWave CDK 17 and CDK 12.5. https://www.baader-p...evue-am-cdk-17/

The latter proves the reducer can deal with flat fields other than by a Petzval so why should it refuse the quadruplet?

The reduction is 0.8 only. I am seriously thinking about it for my 65/420 but for now the relativly little reduction stopped me from buying it. Should I change my mind in the near future I will let you know. I tried the TS-CCD47 and it creates astigmatism everywhere (sample: https://astrob.in/355284/0/) The CCD47 is designed for slower systems without coorrector and naturally low curvature lke RCs.

For the time being I ordered the 2'' to 58mm adapter for astronomical filters on a camera lens. As soon as the weather permits I will try the Tamron 90mm Macro f/2.8 with 7nm Ha-filter to get Heart and Soul in one image.

So you think about converting the f/6.8 474mm to f/5,4 379mm?

 

During my research I listed a few options:

 

Triplets

TS AP 80/480 = TLAPO804 + TSRED279 FPL-53 Triplet, 380mm f/4.7 Eur 800+235 = 1035 Eur

TSAPO71Q 347mm, FPL53-Tripl incl 1-lens. Fluorid corr, f/4,9  Eur 1300

WO 71/420 GT71 Triplet + WO Flat6A II 0.8x  336mm f/4,5 Eur 880+230=1110

WO 71/350 incl. Korrektor FPL-53 Triplet 350mm f/4.9  Eur 1390

TSAPO65Q 420mm f/6.5 FPL53-Triplet w. Flat. Eur 775, 688 at Astroshop.de (I first commented: too long but it finally won the contest)

 

Doublets

TS AP 60/360 + TS-Photoline Flat 1x 360mm f/6 Eur 450+165 = 615

TS AP 72/432 + TSRED279 FPL-53-Duplet, 331mm f/4,7 Eur 430+235 = 665 (my first choice in the doublet list)

TS 60/330 ony at Astroshop, FPL53 Dublet, Flattener unknown 330mm f/5,5 Eur 615

TSAPO72, devidable tube, FLP53-Duplet, TSRED279 316mm f/4,4  Eur 600+335=935

TSAPO80F7 - Duplet w TSRED279 424mm, f/5,5 Eur 550+235=785

WO AP 61/360 + Flattener: FPL-53-Duplet, 360mm, f/5,9 Eur 490+190 = 680 wobbely L-shaped tripod connector

 

I spent some days browsing astro bin images taken with some of the scops and reading about doublet vs. triplet and I phoned TS hotline and astroshop hotline and put a few questions.....

Conlusions (my conclusions, not common wisdom!):

- some doublets proof to be as good a some triplets but this is always for longer focal lenghts

- some triplets seem to be worse than some dublets but a look at the price explains why

- FPL 53 is regarded better than FPL 51

- FCD1 glass seems to be similar to FPL 51 http://www.hoya-opti...sreference.html

- FCD 100 seems to be close but not quite the same as FPL 53 (they put in in paren in the list, whatever that means)

- As soon as you approach f/4 tilt plates are recommended or part of the scope (TSAPO81Q FPL-53-Triplet incl. 3-lens corr. 352mm, f/4,4 comes with a tilt plate)

- shorter focal lenths are more demanding when it comes to CA

- the faster the more critical the focus position

 

My decision then was to stay away from too fast a system and tilt plates and to go for an FPL53 triplet to avoid CA with the short FL. I also want to enjoy the comfort of an included flattener. AND I AM HAPPY with the little toy. Only the dew cap is too short. Hope it helps.


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#33 RogeZ

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Posted 11 September 2018 - 04:04 AM

F/4 scopes are recommended a tilt plate an also at those price ranges the scopes wont be perfectly flat or collimated. Stay away from anything less than F5.

If you want faster than F5 and refractor start saving for an FSQ106EDXIV with reducer.
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#34 luter68

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Posted 11 September 2018 - 10:31 AM

TS states it can. Tele Vue made it for their Petzval types. A Petzval has got a group of lenses relatively far away from the front group, so there is some similarity in the design. There is an article by Baader Planetarium, only available in German where they tested the NPR1073 at the PlaneWave CDK 17 and CDK 12.5. https://www.baader-p...evue-am-cdk-17/

The latter proves the reducer can deal with flat fields other than by a Petzval so why should it refuse the quadruplet?

Right. On the other hand there may be an issue with the backfocus of the given scope (that it is said should be > 120mm). In fact, on the TS page of the Televue corrector, only some of the quadruplets are listed as compatible and the 71mm f/4.9 imaging star (backfocus 66mm) is not listed. So, whether is compatible with a Meade 70Q or with a WO star 71 it should be checked case by case.

I think they are all below 70 mm backfocus.

 


The reduction is 0.8 only. I am seriously thinking about it for my 65/420 but for now the relativly little reduction stopped me from buying it. Should I change my mind in the near future I will let you know. I tried the TS-CCD47 and it creates astigmatism everywhere (sample: https://astrob.in/355284/0/) The CCD47 is designed for slower systems without coorrector and naturally low curvature lke RCs.

For the time being I ordered the 2'' to 58mm adapter for astronomical filters on a camera lens. As soon as the weather permits I will try the Tamron 90mm Macro f/2.8 with 7nm Ha-filter to get Heart and Soul in one image.

So you think about converting the f/6.8 474mm to f/5,4 379mm?

 

No, I was thinking to the 71 f/4.9 imaging star. Now, after thinking better, I realize it would not work. To me, f/5.4 is the maximum speed I want to deal with but, given the cost of the televue reducer, it doesn't make much sense going that way.

Still, if you try it with the 65mm quad, I would certaily like to know how it goes.

Also interested in your test with the Tamron. I have one too (the model without VR) that I like quite a lot for normal use but it is very bad for AP wide open or even one stop closed. However, it may just be my sample. I was thinking of replacing it and would be interesting to see if there is some working well.

During my research I listed a few options:

 

Triplets

TS AP 80/480 = TLAPO804 + TSRED279 FPL-53 Triplet, 380mm f/4.7 Eur 800+235 = 1035 Eur

TSAPO71Q 347mm, FPL53-Tripl incl 1-lens. Fluorid corr, f/4,9  Eur 1300

WO 71/420 GT71 Triplet + WO Flat6A II 0.8x  336mm f/4,5 Eur 880+230=1110

WO 71/350 incl. Korrektor FPL-53 Triplet 350mm f/4.9  Eur 1390

TSAPO65Q 420mm f/6.5 FPL53-Triplet w. Flat. Eur 775, 688 at Astroshop.de (I first commented: too long but it finally won the contest)

 

Yes, I would also add the TS 80/500 superapo or the version with carbon tube. I think both have a superion focuser wrt the 80/480. Cost is, however, higher at arount 1100 Euro without flattener/reducer..

 

Doublets

TS AP 60/360 + TS-Photoline Flat 1x 360mm f/6 Eur 450+165 = 615

TS AP 72/432 + TSRED279 FPL-53-Duplet, 331mm f/4,7 Eur 430+235 = 665 (my first choice in the doublet list)

TS 60/330 ony at Astroshop, FPL53 Dublet, Flattener unknown 330mm f/5,5 Eur 615

TSAPO72, devidable tube, FLP53-Duplet, TSRED279 316mm f/4,4  Eur 600+335=935

TSAPO80F7 - Duplet w TSRED279 424mm, f/5,5 Eur 550+235=785

WO AP 61/360 + Flattener: FPL-53-Duplet, 360mm, f/5,9 Eur 490+190 = 680 wobbely L-shaped tripod connector

 

I spent some days browsing astro bin images taken with some of the scops and reading about doublet vs. triplet and I phoned TS hotline and astroshop hotline and put a few questions.....

Conlusions (my conclusions, not common wisdom!):

- some doublets proof to be as good a some triplets but this is always for longer focal lenghts

- some triplets seem to be worse than some dublets but a look at the price explains why

- FPL 53 is regarded better than FPL 51

- FCD1 glass seems to be similar to FPL 51 http://www.hoya-opti...sreference.html

- FCD 100 seems to be close but not quite the same as FPL 53 (they put in in paren in the list, whatever that means)

- As soon as you approach f/4 tilt plates are recommended or part of the scope (TSAPO81Q FPL-53-Triplet incl. 3-lens corr. 352mm, f/4,4 comes with a tilt plate)

- shorter focal lenths are more demanding when it comes to CA

- the faster the more critical the focus position

 

My decision then was to stay away from too fast a system and tilt plates and to go for an FPL53 triplet to avoid CA with the short FL. I also want to enjoy the comfort of an included flattener. AND I AM HAPPY with the little toy. Only the dew cap is too short. Hope it helps.

It certainly does help, thank a lot. Your conclusions are very similar to mine. For me, it is important to be reasonably fast. If I had a different camera I would actually likely consider the 65/420 too but, in my case, I probably will get the Esprit 80. Later I may or may not see how it works with a TSRED279. It would be a modest  risk as I can always resell the reducer and minimize losses to some tens of Euro. I concur that tilt is likely the biggest problem when going to f/4, bloated stars the next one.

 

CS



#35 the Elf

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Posted 11 September 2018 - 12:11 PM

So, looking forward to your first image then!


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#36 the Elf

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Posted 12 September 2018 - 01:40 AM

OT: Luter, so you have the 2007 model Tamron SP AF DI. It contains 10 elements in 9 groups. I have the 2013 model VC USD (optically identical with the latest waterproof version) made from 14 elements in 11 groups. This is a different lens as the number of elements clearly shows. It proofed exellent as a macro and protrait lens. Curious how it performs with the stars.


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#37 luter68

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Posted 12 September 2018 - 08:30 AM

OT: Luter, so you have the 2007 model Tamron SP AF DI. It contains 10 elements in 9 groups. I have the 2013 model VC USD (optically identical with the latest waterproof version) made from 14 elements in 11 groups. This is a different lens as the number of elements clearly shows. It proofed exellent as a macro and protrait lens. Curious how it performs with the stars.

A search on astobin for "Tamron f/2.8" reveals few pictures. Often the lens is clearly stopped down. With a lens so short front stopping is not feasible without huge vignetting. For me, it would be great if the lens is good wide open (I do not like much the diffraction spikes, but that is me).

If the new model does, then I would love to know.

Good luck with your tests!



#38 bobzeq25

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Posted 12 September 2018 - 09:22 AM

A search on astobin for "Tamron f/2.8" reveals few pictures. Often the lens is clearly stopped down. With a lens so short front stopping is not feasible without huge vignetting. For me, it would be great if the lens is good wide open (I do not like much the diffraction spikes, but that is me).

If the new model does, then I would love to know.

Good luck with your tests!

The cure for diffraction spikes is to stop down with a circular thread adapter.  Most camera lenses like to be stopped down for astro a bit.



#39 luter68

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Posted 12 September 2018 - 10:05 AM

The cure for diffraction spikes is to stop down with a circular thread adapter.  Most camera lenses like to be stopped down for astro a bit.

If you refer with this to a step down ring screwed on the filter thread in front of the lens, this is indeed what I call "front stopping". However, I do not think you can use this method on short FL lenses. I use it on a 200 mm full frame lens (down from 52 to 37mm to get f/5.4) and already causes clear (but still correctable) vignetting on an APS-C sensor (It is basically fine on a 1" sensor).

If you instead mean screwing something on the rear side, yes that would work with all lenses but only if you put the diaphragm at the aperture, that is where the blades are. However, this is possible in very few lenses as the majority (AFAIK) have optical elements behind the blades.



#40 the Elf

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Posted 12 September 2018 - 03:48 PM

A changeable aperture as used in any photo lens must be at a place in the optical path where there is no image but all image information everywhere in the plane. Cropping this plane takes light but no information. Cropping elsewhere removes parts of the image and causes vignetting and it also changes the perspective of the lens (not relevant for astro but for macro). A high quality lens with 12 or more apetrure blades with a curves inside shape may not suffer much from diffraction when stopped down while a cheaper one with only 8 simple blades might suffer a lot. The step down ring is a compromize not as bad as the compromize of too less blades. The lens is corrected for macro and probably far from optimum. It's just a test to quantify the error. On a scale from poor to good: my worst ever attempt on astro imaging was a test shot with the the Sigma 50-500. I knew it would be bad but it was even worse than expected. Bit better, usable at low res was a Milky Way shot with a 17-250 for it was the only lens I carried to the US for that trip. Better than that the out of curiosity attempt to put the RCs reducer behind the refractor: at full HD at a glance not a bad image, on the second look astigmatism. Now my question is: will the Tamron be better or worse? Your bet please, gentlemen!

It is pretty clear that Bob's new scope (*g*) will of course deliver a better quality as it is designed for it. Seriously: I forgot the title of this thread. Yeah, right: "what APO....." The Tamron is none. Who can tell when I put the Ha filter in front (ha-ha-ha the evel elfs laughter). I'll open a new topic on it when I have some images. But for the rest of the week the forecast says: cloudy nights. LOL. And still wating for the filter adapter. Then I will see if the lens hood still can be used that serves as a dew cap. Dew might end the experiment pretty quickly. Not sure if I want to use my GF hairdryer in the garden at 3am in the morning.....

BTW: I did not stop down the Rokinon 16 for this: https://astrob.in/355116/0/


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#41 luter68

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Posted 13 September 2018 - 03:20 AM

A changeable aperture as used in any photo lens must be at a place in the optical path where there is no image but all image information everywhere in the plane. Cropping this plane takes light but no information. Cropping elsewhere removes parts of the image and causes vignetting and it also changes the perspective of the lens (not relevant for astro but for macro). A high quality lens with 12 or more apetrure blades with a curves inside shape may not suffer much from diffraction when stopped down while a cheaper one with only 8 simple blades might suffer a lot. The step down ring is a compromize not as bad as the compromize of too less blades. The lens is corrected for macro and probably far from optimum. It's just a test to quantify the error. On a scale from poor to good: my worst ever attempt on astro imaging was a test shot with the the Sigma 50-500. I knew it would be bad but it was even worse than expected. Bit better, usable at low res was a Milky Way shot with a 17-250 for it was the only lens I carried to the US for that trip. Better than that the out of curiosity attempt to put the RCs reducer behind the refractor: at full HD at a glance not a bad image, on the second look astigmatism. Now my question is: will the Tamron be better or worse? Your bet please, gentlemen!

It is pretty clear that Bob's new scope (*g*) will of course deliver a better quality as it is designed for it. Seriously: I forgot the title of this thread. Yeah, right: "what APO....." The Tamron is none. Who can tell when I put the Ha filter in front (ha-ha-ha the evel elfs laughter). I'll open a new topic on it when I have some images. But for the rest of the week the forecast says: cloudy nights. LOL. And still wating for the filter adapter. Then I will see if the lens hood still can be used that serves as a dew cap. Dew might end the experiment pretty quickly. Not sure if I want to use my GF hairdryer in the garden at 3am in the morning.....

BTW: I did not stop down the Rokinon 16 for this: https://astrob.in/355116/0/

Yeah, the rokinons seem to have a good reputation, even wide open (look at the 135 f/2). The blades of modern lenses are likely to be still be roundish enough just one stop closed. Of all the lenses I have, however, none is good below f/5. It also depends a lot on the specific item. A bump, a little decentering and it is over for AP.



#42 luter68

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Posted 13 September 2018 - 03:32 AM

Thank you very much everyone for the great discussion. It was very helpful to focus on the issue and take a decision. I found Cloudy Nights to be really an amazing place, full of enthusiastic people!!!

 

So, I will go for the Esprit 80 with the original flattener.

Then, a last question: to save weight (and to solve the problem of how eventually stiffly mount my ASI 60/280 guide scope on the Esprit 80), I am looking for an OAG. Any suggestion?

 

The back focus is 55 mm and I have an EFW8 (20mm) and the ASI 183 MMC (6.5 mm), so I have 28.5mm left between EFW and flattener. Later I may want to look for a tilt adapter so I would not want to use really all of the space.

 

The guide camera is an ASI224 and I use 31mm filters.

 

Thanks once more!!



#43 the Elf

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Posted 13 September 2018 - 06:05 AM

You get what you pay for, as always. I own the ZWO and the tilt issue it had is meanwhile fixed by another screw in the front. If comes with a lot of rings and adaptors. You can use either T2 or 2'' on both sides of the OAG and it is T2 for the guide cam.

https://www.highpoin...s-guider-zwooag

 

you probably going to order here:

https://www.teleskop...s-Zubehoer.html

 

Find details in my OAG video. I strongly recommend you get that small 0.5 reducer by TS to get a decent signal for the guide cam!!!!!

https://www.teleskop...tergewinde.html

https://www.teleskop...de-L--18mm.html

 

 

Be prepared for a lot of trial and error until you have a nice configuration. The small reducer should be as close as possible to the exit hole of the stalk and when you are in focus with the guide cam you have to find the right amount of spacer rings to get the main cam in focus, too. TST2Vxxx helps you there. The spacer rings have a ridiculous high price. If you can use T2 for the main cam the rings are cheaper.

 

I ordered a helical focuser for the guidecam, but still waiting.


Edited by the Elf, 13 September 2018 - 06:20 AM.

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#44 luter68

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Posted 13 September 2018 - 09:07 AM

Thank you. Indeed the ASI OAG is what I am currently thinking about.

 

However, this one seems also interesting

 

https://www.teleskop...--L--27-mm.html

 

although it would use nearly all of my backfocus it seems more versatile.

 

Did it happen to you to have difficulties at finding a suitable guide star?

 

I do have one of these reducers from TS. Which guide camera are you using?



#45 the Elf

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Posted 14 September 2018 - 03:06 AM

The bigger one by TS has got a T2 only at the camera side which is less diameter than the 2'' option. If you have a large sensor and a fast scope this might introduce vignetting. At the first glance the rotation option seems nice, but the question is, can you really use it? If the image circle is small the prisme is close to the main sensor and the only place to put it is the long side of the sensor. Now if you rotate the prims and move it to the corners you create vignetting in ond corner and you also create diffraction spikes. With the reducer I already have vignetting and spikes at the long side, so no option for my setup.

I'm using the Lacerta MGEN-II stand alone auto guider. The biggest con on it is the fact that camera and controller are a closed system. You cannot attach any other camera and they only sell this one. It is not bad but there are more sensitive cameras at the market. For that reason I have to plan my imaging in stellarium and write down a few positons, where I find a guide star. That in turn means that you have to measure the size and distance of the guide cam's FOV to enter it in the program. Here is an example of the Crescent with my RC8 and reducer:

OAG-plan.png

 

Right now I'm limited to mag8, but as soon as I have a focusser for the guide cam I hope it will be a bit better.

I do have difficulties finding the star in the field and that is due to the poor goto precision of the mount. The AVX is really a problematic thing and needs a lot of extra efford. During planning I check for a bright star next to my imaging object. After goto alignment (with illuminated cross hair eye piece) I put the camera in and slew to that star. It is never in the center, not remotely. So I slew to the center and then use the sync function in the alignment menu. This makes goto better in the reagion nearby. This decays during the night. If you try again 5 hours later it is again quite a bit off. Plus often the center position saved in the mount data base is not what I like in the center of the image. That in turn means I also select the position in stellarium and write down the RA/dec I like in the center. Then I use the goto RA/dec of the mount to get there and do a few test shots, then save it as a users position in the mount. After that I slew the mount so that the counter weight bar is level and the scope is level and use an angle meter at the bottom of the camera to rotatet it as planned. It needs a few knots in the brain as up is alway in direction to polaris which is different when the object is in the north or south and also when east or west of the meridian. Provided I got it right I slew to the users position saved before and guess what: no star. Last time my rotation was 12° off. Still working on that. I think a good camera rotator and a precise mount will make it easier but right now I decided to put my money in my house and pause the astro investments for a while. As soon as I have a reliable procedure I plan to make another video on that.

As sais before in my PM: you are welcome to an imaging session at the elf's place if you need assistance.


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#46 bobzeq25

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Posted 14 September 2018 - 10:07 AM

Thank you. Indeed the ASI OAG is what I am currently thinking about.

 

However, this one seems also interesting

 

https://www.teleskop...--L--27-mm.html

 

although it would use nearly all of my backfocus it seems more versatile.

 

Did it happen to you to have difficulties at finding a suitable guide star?

 

I do have one of these reducers from TS. Which guide camera are you using?

My solution to the OAG guidestar problem was to bludgeon it to death <smile> with a sensitive guide camera.  In my case (Celestron OAG, needs a ton of backfocus) it's a QHY174mono.  So far that's worked.  I position the takeoff prism along the long edge of the frame, to get in in the "good field" without shadowing.

 

The big chip of the 174 is a waste with most OAGs.  With the Celestron OAG (large takeoff prism), it expands the guidescopes field of view.

 

An alternative for you with the Esprit80, is to spend the money on a really rigid guidescope mount system from ADM accessories.  There's little advantage to the OAG with a small refractor, over that.  It's an easy fix to the guidestar issue.

 

I use a guidescope with my 335mm refractor, OAG with the 910mm.


Edited by bobzeq25, 14 September 2018 - 10:14 AM.

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#47 luter68

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Posted 14 September 2018 - 10:22 AM

My solution to the OAG guidestar problem was to bludgeon it to death <smile> with a sensitive guide camera.  In my case (Celestron OAG, needs a ton of backfocus) it's a QHY174mono.  So far that's worked.  I position the takeoff prism along the long edge of the frame, to get in in the "good field" without shadowing.

 

The big chip of the 174 is a waste with most OAGs.  With the Celestron OAG (large takeoff prism), it expands the guidescopes field of view.

 

An alternative for you with the Esprit80, is to spend the money on a really rigid guidescope mount system from ADM accessories.  There's little advantage to the OAG with a small refractor, over that.  It's an easy fix to the guidestar issue.

 

I use a guidescope with my 335mm refractor, OAG with the 910mm.

I have an ASI224 for guiding. Hopefully, it will be  sensitive enough. Of course, I would be happy using my ASI 60/280 for guiding but, indeed, I am not sure how to mount it rigidly enough as the Esprit 80 has only the finder shoe for that. The lack of the mounting rings on the Esprit has been one of the main reasons I have been so undecided about this scope. Are you thinking of a specific ADM set for this?



#48 bobzeq25

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Posted 14 September 2018 - 04:31 PM

I have an ASI224 for guiding. Hopefully, it will be  sensitive enough. Of course, I would be happy using my ASI 60/280 for guiding but, indeed, I am not sure how to mount it rigidly enough as the Esprit 80 has only the finder shoe for that. The lack of the mounting rings on the Esprit has been one of the main reasons I have been so undecided about this scope. Are you thinking of a specific ADM set for this?

https://www.cloudyni...0/#entry8101332

 

Also see post #20, but that looks difficult to balance.


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#49 luter68

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Posted 14 September 2018 - 04:51 PM

https://www.cloudyni...0/#entry8101332

 

Also see post #20, but that looks difficult to balance.

 

Thanks a lot! Post #20 is my current setup, basically.

 

ASI183MMC + Nikkor200f4

 

It works but the saddle on the heavy side.......

Post #21 looks interesting.

 

i’ll read It through.




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