QHY268M & QHY268C Users Thread (Please share your knowledge and tips)

[AMcD]

16 minutes ago, teoria_del_big_bang said:

Maybe you need to replace the desiccant in the tube ?

@teoria_del_big_bangThanks Steve.  Will the desiccant tube make a difference when the condensation is on the outside of the CMOS window rather than the inside?  

I think the CMOS chamber is OK.  I believe it is the area in front of the CMOS window / in the filter wheel body where there are high levels of humidity, causing condensation to condense on the front of the CMOS window.  I will also check the position inside the chamber with EZCap.

Edited October 1, 2022 by AMcD

[Richard_]

29 minutes ago, AMcD said:

I had one of those astrophotography nights last night that seems to be an endless exercise in problem solving.  First, the battery in my Gemini I was low, causing strange slewing behaviour, and had to be replaced.  Second, as the autumn temperatures decrease the focuser tensioner on the TS152 became looser, causing slippage when pointed at the Zenith, and had to be tightened.  Finally, following the heavy rain, and with humidity at 98%, it would appear that the heater for the window in front of the CMOS chip on the QHY268M was overwhelmed, as condensation formed on the outside of the window (presumably once the temperature gradient between the inside and outside of the window became too acute) ...

I suspect this may be consistent issue for me as the camera / filter wheel are kept permanently in the observatory, which is dry but unheated; at least when there are very high levels of humidity and I attempt to go for a low CMOS temperature (last night -20C).  Does the dew strap solution work consistently @Richard_?  I also wondered about purging the filter wheel and remainder of the imaging train in front of the CMOS window with argon.  I have also read that keeping the camera temperature at parity with the ambient temperature resolves the issue but, of course, at the price of increased noise.

It sounds like last night was a bit of a disaster! But hopefully you have resolved all these issues at once and won't have future sessions ruined I had a similar night the other week, I went back inside and was controlling my rig from my laptop in bed at 1am and the auto focus routine was consistently failing (flat from right to left, then rising to U-shape). Turned out it was a loose grub screw on the focuser coupler which wasn't locking to the focuser shaft. The entire imaging system failed due to a sodding grub screw! 

Anyway, back on track. Yeah, your image shows condensation build up on the window, but which side is the question. Just to confirm, you're cooling your camera to -20°C right? If so, there is really no need to go that cool with this camera. I set mine to -5°C and my 300s darks still look really clean. I've read similar reports when users are using low cooling temperatures mixed with high humidity which results in dew build up on the sensor window. This happened even when users were cooling to -10°C, but when users raised the temperature to -5°C or even 0°C they reported no problems. Also, did you check the humidity inside the sensor chamber for the camera? When I use NINA, the humidity in the sensor chamber is displayed in the camera info. If this is too high (above 70% or so) you can screw in the tube of dessicant to suck some of that moisture out. 

With regards to the dew heater around extension tubes in front of the camera, I can confirm this consistently worked with my ASI533 which dose not have a dew heater in front of the window like the QHY268/ASI2600. Assuming I had a dew issue in the first place, I never saw that issue again after installing the dew heater. 

[teoria_del_big_bang]

3 minutes ago, AMcD said:

@teoria_del_big_bangThanks Steve.  Will the desiccant tube make a difference when the condensation is on the outside of the CMOS window rather than the inside?  

I think the CMOS chamber is OK.  I believe it is the area in front of the CMOS window / in the filter wheel body where there are high levels of humidity, causing condensation to condense on the front of the CMOS window.  I will also check the position inside the chamber with EZCap.

Oh okay, I guess thats a tricky one, the humidity has been very high most of the year.
But as @Richard_ suggests cooling to -5C may help, it does mean taking new darks but worth a try, I don't think there is a big noise issue with this camera and -5 should be fine.

Steve

[AMcD]

57 minutes ago, Richard_ said:

It sounds like last night was a bit of a disaster!

It was!  Bloody button batteries and grub screws.  The focuser tensioner on the TS152 is a giant grub screw and the battery holder in the Gemini I is not user friendly.  Always fun to fiddle with those in the poor lighting of my observatory.

Many thanks as always to you and  @teoria_del_big_bang for your sage advice regarding -5C.  I will try that.  It is not a big issue to re-do the darks given the number of cloudy nights forecast for the next week 😳

If the issue remains, I can add in a dew heater on the imaging train and I will look to purging the area in front of the CMOS window / in the filter wheel body with argon, which is a method I see was mentioned on Cloudy Nights for this issue and that also seems to have worked.

Thanks again.

[AMcD]

P.S. The condensation was definitely on the outside of the window, as I was able to blow it away and dry the window with a bulb blower.

[Richard_]

No problem @AMcD! Yes, I saw the same post on CN and purging with Argon in imaging train (read: filter wheel and spacers) may help with that.

With regards to dessicant, I tried the orange beads which came with the camera last week. It reduced the humidity in the sensor chamber but maybe by 5% or so. Per Shannon's recommendation, I bought some molecular sieve which has been attached to my camera for a few days. There is already a sponge in the dessicant tube to prevent beads from leaving the tube into the camera, but as this molecular sieve is more fine, I added a small layer of cotton linen. Also, the tube is under the camera pointing up so I'm not worried about dust bleeding through via gravity. 

I'll fire the rig up today or tomorrow to check humidity to see if there's a change or not. 

Link to molecular sieve I bought on ebay:

https://www.ebay.co.uk/itm/362072324608?var=631297416033&_trkparms=amclksrc%3DITM%26aid%3D111001%26algo%3DREC.SEED%26ao%3D1%26asc%3D20170504100626%26meid%3D3ee061dbbc9d4e509d81241a73600bc9%26pid%3D100803%26rk%3D2%26rkt%3D15%26mehot%3Dnone%26sd%3D373515840577%26itm%3D631297416033%26pmt%3D1%26noa%3D1%26pg%3D2380057&_trksid=p2380057.c100803.m4236&_trkparms=pageci%3A83f103f3-416b-11ed-953d-8e231c99f78e|parentrq%3A92e0e1401830a4d65cfa9600fffa3cd0|iid%3A1

Edited October 1, 2022 by Richard_

[teoria_del_big_bang]

50 minutes ago, Richard_ said:

No problem @AMcD! Yes, I saw the same post on CN and purging with Argon in imaging train (read: filter wheel and spacers) may help with that.

With regards to dessicant, I tried the orange beads which came with the camera last week. It reduced the humidity in the sensor chamber but maybe by 5% or so. Per Shannon's recommendation, I bought some molecular sieve which has been attached to my camera for a few days. There is already a sponge in the dessicant tube to prevent beads from leaving the tube into the camera, but as this molecular sieve is more fine, I added a small layer of cotton linen. Also, the tube is under the camera pointing up so I'm not worried about dust bleeding through via gravity. 

I'll fire the rig up today or tomorrow to check humidity to see if there's a change or not. 

Link to molecular sieve I bought on ebay:

https://www.ebay.co.uk/itm/362072324608?var=631297416033&_trkparms=amclksrc%3DITM%26aid%3D111001%26algo%3DREC.SEED%26ao%3D1%26asc%3D20170504100626%26meid%3D3ee061dbbc9d4e509d81241a73600bc9%26pid%3D100803%26rk%3D2%26rkt%3D15%26mehot%3Dnone%26sd%3D373515840577%26itm%3D631297416033%26pmt%3D1%26noa%3D1%26pg%3D2380057&_trksid=p2380057.c100803.m4236&_trkparms=pageci%3A83f103f3-416b-11ed-953d-8e231c99f78e|parentrq%3A92e0e1401830a4d65cfa9600fffa3cd0|iid%3A1

I never heard of this being a problem before.
There is a very fine mesh at the bottom of the tube that should  stop this but are you saying people have still had dust from the desicant inside camera ?

I have just checked mine and probably needs changing anyway as the orange beeds are now a dark green. I did not use the supplied desicant but already had some larger beads that are slightly bigger than the hole at the bottom of the tube and made sure all the beads were full beads so hopefully this has not been an issue for me.

What is the advantage of the  ones in the link, are they just better absorption, or are they dust free or semething ?

Steve

[Richard_]

19 minutes ago, teoria_del_big_bang said:

I never heard of this being a problem before.
There is a very fine mesh at the bottom of the tube that should  stop this but are you saying people have still had dust from the desicant inside camera ?

I have just checked mine and probably needs changing anyway as the orange beeds are now a dark green. I did not use the supplied desicant but already had some larger beads that are slightly bigger than the hole at the bottom of the tube and made sure all the beads were full beads so hopefully this has not been an issue for me.

What is the advantage of the  ones in the link, are they just better absorption, or are they dust free or semething ?

Steve

With the regular orange beads provided, there shouldn't be any issue at all. The molecular sieve I ordered have smaller beads and there was a little bit of dust in the packaging, so I wasn't confident that the black sponge already in the dessicant tube would stop smaller particles falling through. 

Just to reiterate, this isn't an issue with the provided orange beads

[Richard_]

15 minutes ago, Richard_ said:

With the regular orange beads provided, there shouldn't be any issue at all. The molecular sieve I ordered have smaller beads and there was a little bit of dust in the packaging, so I wasn't confident that the black sponge already in the dessicant tube would stop smaller particles falling through. 

Just to reiterate, this isn't an issue with the provided orange beads

I've attached some pictures showing the two dessicants side by side. The second picture shows all the dust in the packaging! 

The orange beads are the dessicant provided with the camera. 

The brown beads are the molecular sieve. 

 

37 minutes ago, teoria_del_big_bang said:

What is the advantage of the  ones in the link, are they just better absorption, or are they dust free or semething ?

Steve

From what I've read, molecular sieve can absorb water more quickly than silica gel. So if the relative humidity increases quite quickly, the molecular sieve should be able to absorb the moisture faster than silica gel. On the other hand, gram per gram silica gel can retain more moisture than molecular sieve can, especially at higher relative humidity.

In short, it depends on whether you want the moisture to be absorbed faster, or want to absorb more moisture in long run. This article explains it better. 

https://www.cilicant.com/silica-gel-vs-molecular-sieve/

[Rob_Jn]

Molecular sieve is capable of reducing the humidity to ~20% whereas silica gel is higher, from memory around 40%. The Atik cameras use mol sieve tablets and I think some ZWO cameras too. 4A sieve is usually recommended for moisture absorption but 3A will work.

(not that you need to go down to 20% in this camera 😊)

Edited October 1, 2022 by Rob_Jn

[teoria_del_big_bang]

Thanks @Richard_ & @Rob_Jn for explanation.
I may well order some of the Molecular sieve and kep just in case I have an issue in the future, but as it stands I think I will use the old "If it aint broke then don't fix it" suggestion and stick to the orange beads.

Steve

[Stuart1971]

Can anybody tell me how you can determine the difference between sensor tilt and the need for a flattener…?

I have ordered the flattener for my scope as it’s now needed after getting my QHY268c,Tak FSQ85 scopes does not work well with modern small pixel sensors, as these scopes were designed for large pixel CCD cameras, because of this Takahashi have bought out a new separate flattener to address this issue, which I have ordered, it causes really bad star shapes in the edges of the frame, but according to ASTAP it’s also got bad tilt, and not sure how much of the issue is the need for the flattener, and how much is tilt…🤔🤔

Just wondered if there was a way to tell the difference….

[Richard_]

16 minutes ago, Stuart1971 said:

Can anybody tell me how you can determine the difference between sensor tilt and the need for a flattener…?

I have ordered the flattener for my scope as it’s now needed after getting my QHY268c,Tak FSQ85 scopes does not work well with modern small pixel sensors, as these scopes were designed for large pixel CCD cameras, because of this Takahashi have bought out a new separate flattener to address this issue, which I have ordered, it causes really bad star shapes in the edges of the frame, but according to ASTAP it’s also got bad tilt, and not sure how much of the issue is the need for the flattener, and how much is tilt…🤔🤔

Just wondered if there was a way to tell the difference….

With ASTAP, you can either have a triangle or square which shows HFR at each corner and in the centre. I prefer to work with the square to represent each corner of the sensor.

If the HFR is the same for all four corners but higher compared the centre, that means you either need a field flattener or your back focus distance needs to be addressed. If you have a back focus issue, you can increase/decrease the distance until HFR is approximately same for all four corners and the centre. If you don't have a field flattener, changing the back focus will not create absolute flat stars at edges (but this depends on the scope and size of sensor). 

If you have two corners which have a higher HFR than the opposing two corners, that means one side of the sensor is closer to the focal point than the other corner, and therefore you have tilt. 

I would resolve the tilt issue first before addressing the back focus distance. 

[Stuart1971]

44 minutes ago, Richard_ said:

With ASTAP, you can either have a triangle or square which shows HFR at each corner and in the centre. I prefer to work with the square to represent each corner of the sensor.

If the HFR is the same for all four corners but higher compared the centre, that means you either need a field flattener or your back focus distance needs to be addressed. If you have a back focus issue, you can increase/decrease the distance until HFR is approximately same for all four corners and the centre. If you don't have a field flattener, changing the back focus will not create absolute flat stars at edges (but this depends on the scope and size of sensor). 

If you have two corners which have a higher HFR than the opposing two corners, that means one side of the sensor is closer to the focal point than the other corner, and therefore you have tilt. 

I would resolve the tilt issue first before addressing the back focus distance. 

No backfocus issue as I don’t have the flattener yet….🤔 just bd corner stars due to needing one 👍🏻

[Stuart1971]

46 minutes ago, Richard_ said:

With ASTAP, you can either have a triangle or square which shows HFR at each corner and in the centre. I prefer to work with the square to represent each corner of the sensor.

If the HFR is the same for all four corners but higher compared the centre, that means you either need a field flattener or your back focus distance needs to be addressed. If you have a back focus issue, you can increase/decrease the distance until HFR is approximately same for all four corners and the centre. If you don't have a field flattener, changing the back focus will not create absolute flat stars at edges (but this depends on the scope and size of sensor). 

If you have two corners which have a higher HFR than the opposing two corners, that means one side of the sensor is closer to the focal point than the other corner, and therefore you have tilt. 

I would resolve the tilt issue first before addressing the back focus distance. 

Also how can I change back focus if I don’t have a flattener, there is nothing to change backfocus from surely, the focus point is the focus point….🤔🤔

[Stuart1971]

Just been in the garage for an hour and knocked this up as per the @ollypenrice idea for a tilt jig, I liked the idea of the camera at the top method for a couple of reasons, it will eliminate any other tilt other than sensor tilt, like sag, and no need to worry about how to support the camera while rotating, just need to find a suitable laser and then fasten that..

The tilter I am ordering is the Baader UFC version to fit on my filter slide, which has push pull screws on the sides so will be simple to adjust…similar to the Geurd Newman version.

Also where at the sensor should I point the laser, obviously not at the centre, so am guessing about 2/3rds the way across so the beam does not leave the chip surface when rotating…?? 
 

[Richard_]

1 hour ago, Stuart1971 said:

Also how can I change back focus if I don’t have a flattener, there is nothing to change backfocus from surely, the focus point is the focus point….🤔🤔

Oh, I thought the only refractors where back focus wasn't critical were quadruplets and petzval designs. Are the Tak FSQs in either one of those categories or a triplet? 

[Stuart1971]

7 minutes ago, Richard_ said:

Oh, I thought the only refractors where back focus wasn't critical were quadruplets and petzval designs. Are the Tak FSQs in either one of those categories or a triplet? 

Yes it’s a quadruplet..👍🏻

but any refractor triplet or doublet with no flattener fitted does not have any backspace issues, and not critical as you just rack focuser to where ever it’s in focus, you have no choice where this focus point is…and that’s it

it’s only with flatteners and reducers fitted where you need the correct back focus from said reducer or flattener…to get correct star shapes…

Edited October 1, 2022 by Stuart1971

[teoria_del_big_bang]

2 minutes ago, Stuart1971 said:

Yes it’s a quadruplet..👍🏻

but any refractor triplet or doublet with no flattener fitted does not have any backspace issues, and not critical as you just rack focuser to where ever it’s in focus, you have no choice where this focus point is…and that’s it

it’s only with flatteners and reducers fitted where you need the correct back focus from said reducer or flattener…to get correct star shapes…

That would be my understanding too 🙂 

Steve

[Stuart1971]

Just now, teoria_del_big_bang said:

That would be my understanding too 🙂 

Steve

Yes, I am not sure what he means with regards to critical backspacing when no flattener or reducer is fitted….makes no sense to me, but then I am not the most clued up on this sort of thing….🤔🤔

[Richard_]

3 minutes ago, Stuart1971 said:

Yes, I am not sure what he means with regards to critical backspacing when no flattener or reducer is fitted….makes no sense to me, but then I am not the most clued up on this sort of thing….🤔🤔

What you said above makes sense, it's just that I'm so used to the whole 55mm back focus distance with that it's usually the distance I aim to achieve. 

[ollypenrice]

25 minutes ago, Stuart1971 said:

Just been in the garage for an hour and knocked this up as per the @ollypenrice idea for a tilt jig, I liked the idea of the camera at the top method for a couple of reasons, it will eliminate any other tilt other than sensor tilt, like sag, and no need to worry about how to support the camera while rotating, just need to find a suitable laser and then fasten that..

The tilter I am ordering is the Baader UFC version to fit on my filter slide, which has push pull screws on the sides so will be simple to adjust…similar to the Geurd Newman version.

Also where at the sensor should I point the laser, obviously not at the centre, so am guessing about 2/3rds the way across so the beam does not leave the chip surface when rotating…?? 
 

It isn't dead easy to align the laser precisely with the simple fixation that I used so I just went for more or less the centre. Why not? The angle of the reflecting surface (the chip) is the same right across so I can't see why it would matter. In my thinking the consequences of a tilted chip affect the image asymmetrically because all parts of the light cone create all parts of the image. In the case of the (roughly) point source of the laser only the angle of the reflecting surface matter. I'll happily stand corrected.

Olly

[Stuart1971]

6 minutes ago, ollypenrice said:

It isn't dead easy to align the laser precisely with the simple fixation that I used so I just went for more or less the centre. Why not? The angle of the reflecting surface (the chip) is the same right across so I can't see why it would matter. In my thinking the consequences of a tilted chip affect the image asymmetrically because all parts of the light cone create all parts of the image. In the case of the (roughly) point source of the laser only the angle of the reflecting surface matter. I'll happily stand corrected.

Olly

I have no idea why not, as I am still trying to get my head around the idea, I just assumed,  probably wrongly, that the centre would not be good, as again I wrongly assumed that the centre would not move, just spin on the spot during rotation, and not show the error,  and if tilt was from one side to another the centre would stay pretty much in the same spot, but I am probably looking at all this totally wrong…🤯🤯

Edited October 1, 2022 by Stuart1971

[ollypenrice]

1 hour ago, Stuart1971 said:

I have no idea why not, as I am still trying to get my head around the idea, I just assumed,  probably wrongly, that the centre would not be good, as again I wrongly assumed that the centre would not move, just spin on the spot during rotation, and not show the error,  and if tilt was from one side to another the centre would stay pretty much in the same spot, but I am probably looking at all this totally wrong…🤯🤯

Say your chip is wildly tilted from horizontal like this :   \      A beam arriving from below will be reflected downwards towards the left. If you turn the chip through 180 degrees so it is angled like this  /   it will reflect the same incoming beam downwards towards the right.  That is the test you are performing with the jig. I can't see that it matters where the incident beam hits the chip.

Olly

Edited October 1, 2022 by ollypenrice
typo

[AMcD]

11 hours ago, Richard_ said:

Yes, I saw the same post on CN and purging with Argon in imaging train (read: filter wheel and spacers) may help with that

I think it will be useful during periods of very high humidity.  I ran the camera tonight at -5C over a period during which the AAG Cloudwatcher recorded a rise in humidity from 60% to 72% and there was no sign of condensation.  I would have continued the experiment and waited for the humidity to hits its forecast of 94% later, but I really need to get some sleep tonight😂

The humidity last night touched 98% according to the Cloudwatcher and 100% according to the PPBA environmental sensor and, as you noted, I had the camera cooled far more than is necessary. As such, I suspect if the risk of condensation on the outside of the sensor window is at its greatest at very high humidity readings and that an argon purged imaging train may assist in those situations, if reducing the cooling target does not eliminate the issue completely.