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Imaging with the 130pds


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halli, on 10 Jan 2016 - 10:21 AM, said:

Thanks for the advice Rob.  

I have bought an A3 LED display for flats and am experimenting with this.  Because of the shutter on the 383 it means that the right amount of light reduction needs to be made to increase the exposure time -  which is a bit fiddly.  Unfortunately the panel can be dimmed but does not dim enough !  Its a question of diffusing the light enough to get to the right exposure I guess. I am also going to look at the T shirt method outdoors but again its getting the right thickness of material to get a long enough exposure !  Bring back AV DSLR flats anyday !

I believe a figure of 25-30k ADU and above 5s should be achieved  to avoid the shutter affect ?

Wrt the coma corrector yes the drawtube focusser scews arent the best and I thought of replacing the complete unit which holds the screws  as it is difficult to tighten the screws with the filter wheel in situ as it is. Haven't researched this yet though.  

From the Atik site the backfocus for the 383 is quoted as 17mm which I assume is from the chip to the 383 mating interface - I guess this is the distance I add to the EFW thickness and then add the CC internal distance to the lens and then also add a spacer if required to get 55mm     Does this sound about right to you ?

For dimming your panel, just use a few sheets of copier paper.

In regard to avoiding the shutter, your flat length should be at least 8 seconds - which is a bit more conservative than the 6 seconds quoted by Atik - this is especially true when binning. If you are thinking of replacing the thumbscrews, you will have to come up with your own bespoke threaded solution becuase compression rings should be avoided at all costs (they are the devils work!). I had to produce my own adaptor by allen bolting an M48 thread to the pushfit adaptor - that allowed me to mount the Baader CC internally in the drawtube via its M48 thread... and to get the SW CC in there I literally had to hacksaw and file off its collar (only for the brave!... or mad).

The backfocus for the 383 is 17.5mm I believe, the mechanical drawing for the camera can be found on the Atik website.

In regard to the correct ADU levels, aim on the low side - between 16,000  and 20,000 max ADU (not average). Do not trust the figures given by artemis capture, instead load the test flat into Maxim DL (if you have it) and change information mode to "Area", the maximum ADU value shown there is the one you should be working with. I only found that out after trial and error (yes... lots of error!). :)

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Thanks Rob - looks like some really useful info there - much appreciated !

I have used the SGP flat calibration wizard to provide the exposure for a given ADU target  figure but not sure how accurate it is though - unfortunately I do not have Maxim

I  am in the process of trying to connect a skywatcher CC to my EFW2 filter wheel.  My understanding is that the scope side of the cc is push fit into the draw tube and the other side is M48 male for the filter wheel/camera.  I believe I need a M54/M48 adapter to connect to  the EFW2 which I am struggling to source !

Not sure if I can visualize your set up with the internally mounted CC.

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This is what I mean by a bespoke, all M48 threaded solution (with internally mounted CC and tilt adjustment):

post-5513-0-13848900-1452723682_thumb.jp

post-5513-0-56646600-1452723691_thumb.jp

post-5513-0-02691200-1452723702_thumb.jp

Its not the kind of thing you can buy off the shelf, you have to buy the separate components and fit them together yourself (requires a bench drill, taps and small countersunk hex screws). Bonus being it can be fitted to any 2" skywatcher newtonian focuser, so you can chop and change at will - and it opens up threaded collimation, which is far more repeatable and reliable (though you do need to remember to remove the CC first.... otherwise its metal on glass... not good!).

However.... there is another way you can have an internally mounted CC (though it has to be the Baader), and that is to get a dovetail pushfit adaptor - which would be much better than the straight barrel versions. This one has a 2" fiilter thread scope side, so that is where you would situate your CC. Reason why I said it needs to be Baader is because you can remove the T thread component, just leaving an M48 cell (which is what is inside my adaptor).

http://www.teleskop-express.de/shop/product_info.php/info/p2742_TS-Optics-Adaptor-2--to-T2---low-profile---dovetail.html

The only downside to that is its only available in a T2 camera side fitting, so you would need a T2-M48 adaptor to get it to fit your filter wheel (and losing a bit more spacing to play with in the process).

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and to get the SW CC in there I literally had to hacksaw and file off its collar (only for the brave!... or mad).

In regard to the correct ADU levels, aim on the low side - between 16,000  and 20,000 max ADU (not average). 

Kudos to doing the hacksawing, Rob - I chickened out at this point, although I did hacksaw off 15 mm from the OTA at the primary end of my 150 PDS to stop the focuser causing the odd star shapes! Believe me, I was sweating over that one ;)

But why the 16,000 to 20,000 max ADU for the KAF 8300 flats? I've not come across a compelling reason for this in my 'net travels. I'm sure that your experience shows this to be correct, but is there an engineering explanation?

Cheers,

Paul

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But why the 16,000 to 20,000 max ADU for the KAF 8300 flats? I've not come across a compelling reason for this in my 'net travels. I'm sure that your experience shows this to be correct, but is there an engineering explanation?

Reason is becuase I was having an awful time trying to get my 383 to calibrate properly a few months ago when I got the Star 71 - the flats were over correcting by a long way (giving bright corners). That was with an average level of 26,000 (1/3 histogram in Artemis), so I backed it off to 20,000 maximum level instead and the problem went away immediately. Ive just checked an old 130pds flat, and that was just under 22k maximum - so its in that genereal ball park area (26k+ is a bit high). Both scopes have a completely different vignetting pattern, so there will be some element of experimentation.

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Reason is becuase I was having an awful time trying to get my 383 to calibrate properly a few months ago when I got the Star 71 - the flats were over correcting by a long way (giving bright corners). That was with an average level of 26,000 (1/3 histogram in Artemis), so I backed it off to 20,000 maximum level instead and the problem went away immediately. Ive just checked an old 130pds flat, and that was just under 22k maximum - so its in that genereal ball park area (26k+ is a bit high). Both scopes have a completely different vignetting pattern, so there will be some element of experimentation.

Odd. That's just the point of doing the flats in the first place. As I posted before, because the correction is normalised and multiplicative, as long as the sensor is reasonably linear and the flat is not clipped at either end, it should not matter...

But obviously the range does matter, and your images are a testament to your experience :)

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Really excited to be getting my 130 today...until I found this loose in the box, a box with absolutely no damage I might add.

post-36192-0-42338800-1453293815_thumb.j

It's completely sheared off in the focuser. Doesn't fill me with confidence in Skywatcher's quality control.

Edited by richyrich_one
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Youre going to need to get that sheared bit out somehow, if the threads arent wrecked so you can try gripping and turning the sheared bit wearing a rubber glove, or with the eraser end of a pencil.  Remember: Righty tighty, lefty loosen (you dont want to send it in further!).

Hopefully you should be able to get it out far enough so you can remove it. It looks like you have quite a lot of thread left on your locking screw, so there is probably only a few mm in there. Might be a good idea to smooth off the end the screw with a fine file or some emry paper if its a bit rough.

Failing that, send the scope back from whence it came and get a replacement.

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I did have a little go at trying to remove it but then I thought I shouldn't have to be doing this. I was expecting some tweaking to get the best from it but...

FLO sorting a swap out on Friday hopefully. I was hoping they'd say keep the broken one for your trouble but oh well. 

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Hello all. I'd been imaging with a SW150p for the past three years but wanted something with a bit more FOV. I opted for the 130pds as I could use my existing SW CC and heard great reports of its performance for AP. I've recently started doing some narrowband imaging after modding my 350d (ir/uv removal and CFA debayering). This little scope is an absolute joy :headbang: Just wanted to share my efforts from the other night. Clear skies folks.

Rosette Nebula mono Ha

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Well FLO delivered...Literally:icon_biggrin:

First light has been a while, what with my EQ direct cable DOA.  No problems balancing with the DSLR.

Had a quick go this morning using the synscan handset...Archturus. First thing is the focuser intrusion, much more noticable on the TIF version for some reason.

What are my options to eliminate this? From what I've gathered from this thread...

1. Mount the MPCC into the draw tube some how to facilitate getting the camera further in and so having to rack out more to get focus. Sounds complex trying to get the spacing correct.

2. Chop down the inner end of the draw tube. Could you then potentially rack the draw tube out too far past the rollers at the inner end of the focusser mechinism?

Is there a cheap non-hacksawing option I've missed?:unsure:

Single__2016-01-25_04-47-49_0002_ISO800_

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58 minutes ago, richyrich_one said:

Well FLO delivered...Literally:icon_biggrin:

First light has been a while, what with my EQ direct cable DOA.  No problems balancing with the DSLR.

Had a quick go this morning using the synscan handset...Archturus. First thing is the focuser intrusion, much more noticable on the TIF version for some reason.

What are my options to eliminate this? From what I've gathered from this thread...

1. Mount the MPCC into the draw tube some how to facilitate getting the camera further in and so having to rack out more to get focus. Sounds complex trying to get the spacing correct.

2. Chop down the inner end of the draw tube. Could you then potentially rack the draw tube out too far past the rollers at the inner end of the focusser mechinism?

Is there a cheap non-hacksawing option I've missed?:unsure:

 

You missed one, but it still involves the hack-saw: I chopped 15 mm off of my OTA at the primary end and re-drilled the four cell mounting holes in my 150 PDS for the same reason.

The advantage of this over the focuser hack is that I could use the tripod to hold the tube while I did the dirty deed. :) The whole job took less than two hours.

Edited by Pompey Monkey
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Hmm...Thanks Paul.

I was hoping for a non-destructive option. I like to be able to "undo" if at all possible.:icon_biggrin:

If we are only talking 15mm, is moving the primary with longer screws a neater way? I'm not that familiar with the cell construction so will have to investigate.

Curious, where did you get the 15mm calculation from?

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9 hours ago, richyrich_one said:

Hmm...Thanks Paul.

I was hoping for a non-destructive option. I like to be able to "undo" if at all possible.:icon_biggrin:

If we are only talking 15mm, is moving the primary with longer screws a neater way? I'm not that familiar with the cell construction so will have to investigate.

Curious, where did you get the 15mm calculation from?

Good old engineering judgement:

I'd read that 10 mm off the focuser would fix the "bitten" star feature. Another 5 mm made sure* :)

I'd also picked up my 150 PDS OTA from Astroboot for £113.50, including postage (Brand new, with just a tiny scratch on the tube). So it would only be a little bit painful if it all went wrong. But how could it go wrong? It's just metal tube and some mirrors! :)

*Of course I checked that I would still be able to reach focus first!

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On 13/01/2016 at 22:29, Uranium235 said:

This is what I mean by a bespoke, all M48 threaded solution (with internally mounted CC and tilt adjustment):

post-5513-0-13848900-1452723682_thumb.jp

post-5513-0-56646600-1452723691_thumb.jp

post-5513-0-02691200-1452723702_thumb.jp

Its not the kind of thing you can buy off the shelf, you have to buy the separate components and fit them together yourself (requires a bench drill, taps and small countersunk hex screws). Bonus being it can be fitted to any 2" skywatcher newtonian focuser, so you can chop and change at will - and it opens up threaded collimation, which is far more repeatable and reliable (though you do need to remember to remove the CC first.... otherwise its metal on glass... not good!).

However.... there is another way you can have an internally mounted CC (though it has to be the Baader), and that is to get a dovetail pushfit adaptor - which would be much better than the straight barrel versions. This one has a 2" fiilter thread scope side, so that is where you would situate your CC. Reason why I said it needs to be Baader is because you can remove the T thread component, just leaving an M48 cell (which is what is inside my adaptor).

http://www.teleskop-express.de/shop/product_info.php/info/p2742_TS-Optics-Adaptor-2--to-T2---low-profile---dovetail.html

The only downside to that is its only available in a T2 camera side fitting, so you would need a T2-M48 adaptor to get it to fit your filter wheel (and losing a bit more spacing to play with in the process).

Hi Rob,

 

I'm looking at this adapter from TS. What would be the advantage really compared with the straight barrel version?

E.

 

 

 

 

 

 

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Which adaptor are we talking about? My threaded solution or the dovetail adaptor?

The advantage of a dovetail over a straight barrel is that it "pulls" itelf tight to the EP holder when you do up the thumbscrews (becuase its a dovetail), whereas the straight barrel adaptor can still "pop" out a bit under the weight of a heavy camera - leading to tilt in the focal plane.

If you have one of the spare SW dovetail 1.25" EP adaptors in your bits box (they often come with SW scopes), pop it in and try it - you will see what im on about straight away. 

Its a pretty cheap adaptor from TS, so worth a punt (even though its designed for their rotation system). Give us a week and I might get one in to test the water as it were....  worst case scenario would be that the thumbscrew holes would need to re-drilled (moved up a bit) if the dovetail is a bit short (hard to see it in the photo).

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54 minutes ago, Uranium235 said:

Which adaptor are we talking about? My threaded solution or the dovetail adaptor?

The advantage of a dovetail over a straight barrel is that it "pulls" itelf tight to the EP holder when you do up the thumbscrews (becuase its a dovetail), whereas the straight barrel adaptor can still "pop" out a bit under the weight of a heavy camera - leading to tilt in the focal plane.

If you have one of the spare SW dovetail 1.25" EP adaptors in your bits box (they often come with SW scopes), pop it in and try it - you will see what im on about straight away. 

Its a pretty cheap adaptor from TS, so worth a punt (even though its designed for their rotation system). Give us a week and I might get one in to test the water as it were....  worst case scenario would be that the thumbscrew holes would need to re-drilled (moved up a bit) if the dovetail is a bit short (hard to see it in the photo).

Yes, I meant the dovetail adaptor.  Keep us posted if you get and try one!

 

cheers

E.

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On 25/01/2016 at 18:07, Pompey Monkey said:

Good old engineering judgement:

I'd read that 10 mm off the focuser would fix the "bitten" star feature. Another 5 mm made sure* :)

I'd also picked up my 150 PDS OTA from Astroboot for £113.50, including postage (Brand new, with just a tiny scratch on the tube). So it would only be a little bit painful if it all went wrong. But how could it go wrong? It's just metal tube and some mirrors! :)

*Of course I checked that I would still be able to reach focus first!

By moving the mirror, by which ever means, could there be a problem with illumination of the secondary?

It's just come to me...would it be plausible to create a cutout in the focuser of say 10mm deep but fading to the edges so as to maintain the usability of the focuser and also keep the intrusion to a minimum? Oh what to do...!:unsure:

Something like this...Focuser.thumb.png.2c874868436dd3242d021b

Looking for the perfect solution when one probably doesn't exist...Whatever I do it's looks like I'm dusting off the hacksaw.

 

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7 minutes ago, richyrich_one said:

By moving the mirror, by which ever means, could there be a problem with illumination of the secondary?

It's just come to me...would it be plausible to create a cutout in the focuser of say 10mm deep but fading to the edges so as to maintain the usability of the focuser and also keep the intrusion to a minimum? Oh what to do...!:unsure:

Something like this...Focuser.thumb.png.2c874868436dd3242d021b

Looking for the perfect solution when one probably doesn't exist...Whatever I do it's looks like I'm dusting off the hacksaw.

 

Morning Richie,

Funnily enough, I only posted about this in another thread just last night:

 

"15 mm movement on a 750 mm focal length telescope is a 2% radius = 4% loss of light due to spillage past the secondary, assuming it was fully illuminated in the first place. I can live with that :)

As for vignetting, I would hope the telescope manufacturers would design for none with the focuser fully extended. I certainly don't see evidence for extra vignetting on my flats.

In summary, a small longitudinal movement of the primary is unlikely to have a critical effect on the optical path."

 

I do have the 150 PDS, but the principle is be the same. It's all just triangles.

As for the scooping out of the focuser tube.. Well you could always try it and report back your results... :)

Edited by Pompey Monkey
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Thanks Paul, you are a wealth of information. I didn't really want to dismantle the focuser if I could help it.

2 minutes ago, Pompey Monkey said:

As for the scooping out of the focuser tube.. Well you could always try it and report back your results... :)

How did I know you were going to say that?:icon_biggrin:

 

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Took the mirror cell apart and I've managed a 15mm forward position of the primary. I had to replace the existing collimation screws, M5x20, with M5x40. I also added M5 connector nuts to get the 15mm spacing and with an M5 washer(so could be 16mm forward) was able to use the existing springs. Just a shame I couldn't use the existing locking screws. And it's all undoable!:icon_biggrin:

Collimated nicely and raring to go. *IF* we get something close to a clear sky I can test focus. Should it prove too much adjustment I can always trim down the connector nuts.

There is a perfect solution after all!

IMG_20160127_122516.thumb.jpg.5243dc7a37

(Mirror removed for both clarity and sanity)

 

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