The EQ3 DSO Challenge

[Art Gecko]

2 hours ago, Peco4321 said:

Not sure really as I have a polar scope fitted and get Polaris right in the circle but 30 seconds seems to be my limit. The tripod is level so not sure what else to check. 

I'll send a flat later. 

My first thought is, have you checked to see if your polar-scope is properly centered in the mount? If it's only slightly out it will impact your alignment quite a lot.

To check it... centre it on a star (or distant object.. You can do this during in the day, I used the tip of a TV areal)... Then move your RA axis through 180 degrees... if the target object moves off centre... that's where the problem lies!... Use an allen key to adjust it so the target object moves half way back the the centre... then re-centre it and do the 180 flip again.... repeat this procedure until the target object stays exactly in the centre when you do the 180 flip... then when you polar align, it should be pretty bang on and you should be able to get a minute or more on individual subs (provided there are no vibrations, wind etc... the normal problems for everyone!!)

HTH Art.

[Peco4321]

45 minutes ago, Art Gecko said:

My first thought is, have you checked to see if your polar-scope is properly centered in the mount? If it's only slightly out it will impact your alignment quite a lot.

To check it... centre it on a star (or distant object.. You can do this during in the day, I used the tip of a TV areal)... Then move your RA axis through 180 degrees... if the target object moves off centre... that's where the problem lies!... Use an allen key to adjust it so the target object moves half way back the the centre... then re-centre it and do the 180 flip again.... repeat this procedure until the target object stays exactly in the centre when you do the 180 flip... then when you polar align, it should be pretty bang on and you should be able to get a minute or more on individual subs (provided there are no vibrations, wind etc... the normal problems for everyone!!)

HTH Art.

I did do this but may do it again just to check.

 

Here's a flat, camera left connected to scope till the next day, changed setting to AV and with a white pillow case over the end of scope pointing skywards (it was a bright day).  RAW flat and one saved as Jpg attached.

In dss can I load the stacked Tiff and add flats and re-stack or do I have to start all over again?

 

 

IMG_3529.CR2

[Art Gecko]

25 minutes ago, Peco4321 said:

camera left connected to scope till the next day, changed setting to AV and with a white pillow case over the end of scope pointing skywards (it was a bright day).  RAW flat and one saved as Jpg attached.

In dss can I load the stacked Tiff and add flats and re-stack or do I have to start all over again?

Hmmm there's nothing wrong with taking flats the next day... that's actually a pretty good method.. but there's definitely something not right with that flat... it should be slightly darker in the corners not all along the top!... Why are you changing the settings to AV, what does that do? I have a Nikon not a Canon but the only thing I alter when I take flats is the exposure length... Have you tried taking flats without changing the settings?

[Stub Mandrel]

The new-style reticles are good for up to 120 seconds.

[Peco4321]

I will have a go next time just changing exposure length to much shorter, I read something about doing that, but also read about changing to AV mode, so many views and methods

Will I be able to just add the flats to the DSS stacked TIFF result file, or start all over again?

[Stub Mandrel]

I use AV mode at the same iso and it works very well.

You will need to restack, but you may  be able to reuse the flats if you don't suffer dust bunnies and have a consistent setup.

Edited June 28, 2017 by Stub Mandrel

[Art Gecko]

1 hour ago, Peco4321 said:

I will have a go next time just changing exposure length to much shorter, I read something about doing that, but also read about changing to AV mode, so many views and methods

Will I be able to just add the flats to the DSS stacked TIFF result file, or start all over again?

 

31 minutes ago, Stub Mandrel said:

I use AV mode at the same iso and it works very well.

You will need to restack, but you may  be able to reuse the flats if you don't suffer dust bunnies and have a consistent setup.

I'm not saying it's a bad method, just suggesting that it may be the wrong method in this case.. It's the only obvious change to the setup that may have caused that odd looking flat... at least worth considering?

Yeah, as Neil says, you will need to start the stack from scratch, as the flats are stacked first then the master flat subtracted from each individual sub in the stacking software

[mikey2000]

I've been using the same old flats for months now.   I made them with a white T-shirt over the scope, aimed at a clear blue sky with the camera correctly focussed and held at its usual orientation in the eyepiece holder.  I use Av mode and the same ISO as when imageing, rattled off about 20 of them (raw) then threw them in with some light frames in DSS.  

 

I noticed DSS made a master_flat.tiff.   As I always use the same ISO and put the camera in the same orientation, I seem to be getting good repeatable results.

 

My flats definitely show a slightly off-centre circular shape. I can't imagine why you would get a straight line across a flat file with a circular aperture telescope...

 

I know flats are supposed to correct for dust bunnies on the sensor/mirror etc but I seem to be keeping things clean enough that I don't need to retake more flats.

 

this will of course change if I turn the camera around a bit as my circular shape isn't quite central in the photo.

[bobro]

Peter's flat shows as taken at ISO3200 and 1/4096 sec exposure. I guess the speed is as fast as the camera will go. Perhaps the shutter is a bit sticky at this fast speed. In any case it looks a bit overexposed - a good plan is to have the histogram around the mid point.

Flats don't need to be taken at the same ISO as images (I previously thought flats needed to be taken at the same ISO as images but was corrected by someone with more knowledge and did some tests that showed flats worked irrespective of the ISO used). So I suggest reducing the shutter speed and ISO if necessary in order to obtain flats with roughly a mid point on the histogram.

[Art Gecko]

5 minutes ago, bobro said:

Peter's flat shows as taken at ISO3200 and 1/4096 sec exposure. I guess the speed is as fast as the camera will go. Perhaps the shutter is a bit sticky at this fast speed. In any case it looks a bit overexposed - a good plan is to have the histogram around the mid point.

Flats don't need to be taken at the same ISO as images (I previously thought flats needed to be taken at the same ISO as images but was corrected by someone with more knowledge and did some tests that showed flats worked irrespective of the ISO used). So I suggest reducing the shutter speed and ISO if necessary in order to obtain flats with roughly a mid point on the histogram.

I think you may have cracked it there Bob, well spotted!!

[mikey2000]

About polar alignment....   It's definitely important to make sure the polar scope is centralised (by using the RA rotation method described above)

 

also, when it is centralised, you need to work out which way is up/down in the reticle so the target circle is in the right place.   It's highly unlikely your reticle is exactly the right way up.   Mine was nearly 45 degrees out when first installed.   It fell apart when I was adjusting it and I managed to put it back together almost the right way up but I still need to rotate the RA axis about 10 degrees to get the 12 o'clock mark at the top.

 

how to know where "up" is in a polarscope?

 

aim the polar scope at a distant TV mast or something similar. Centre the middle cross hair on the distant object.   Then use the Az adjust bolt to raise the axis.   If the polar scope reticle is perfectly up/down, the distant target should sit on the 6 o'clock position.  If it misses (left or right of 6 o'clock) you need to rotate the RA axis and try again.   Keep going at this until the reticle is moving nicely up/down

 

(of course, it needs to be nice and level for this to work...)

make a note of where the RA axis has ended up so you can go straight to the position next time.

[mikey2000]

Peco - I wonder if your camera can link up to the SharpCap application (or maybe you have a supported webcam).  The Polar Align routine in SharpCap is extremely quick and seems to be nicely accurate.

[Stub Mandrel]

One zillion times easier with the new reticle, you set the cross-hairs vertical/horizontal, use Polarfinder to tell you where to put polaris on the circle and there's a crib in the corner telling you which diameter ring to use for the year.

You can download a new-style reticle for polar finder here:

http://www.stubmandrel.co.uk/astronomy/123-new-style-reticle-for-polarfinder

My home made goto box displays the correct position:

Edited June 28, 2017 by Stub Mandrel

[mikey2000]

Other thoughts about the polar finder..... I find it rather hard to use physically.  I'm at 51N and looking through the scope involves kneeling on the ground, removing my glasses (there is no rubber shield on the eyepiece) and somehow reaching around to the Az/Alt adjustment bolts to make the adjustment without losing my balance.  I greatly prefer the SharpCap method where the 'looking' and fine adjustment is all done on the computer screen nearby.  I use the polar scope for the initial rough alignment but the fine tuning is from SharpCap.

 

As well as Polar Finder, there is a handy iphone app "Polar Scope Align" which has the new Skywatcher scope included.  It has a handy utility to offset for misaligned reticles.  (maybe available on android too, but I'm not sure)

[Art Gecko]

I use PolarAlign on iPhone... can't say I've had any problem with it...

 

[Peco4321]

Great advice from everyone on both polar alignment and flats, thanks. Lots to try next time out. 

[rotatux]

21 hours ago, Peco4321 said:

polar scope fitted and get Polaris right in the circle

Not enough: you have to rotate the polar scope to either 1/ match your local longitude + date + hour, or 2/ match other constellations around NCP (such as Ursa Minor/Major and Cassiopeia).

Otherwise you may be up to 2x40' (1.33°) offset from NCP, and that might explain your trouble.

[Peco4321]

5 hours ago, rotatux said:

Not enough: you have to rotate the polar scope to either 1/ match your local longitude + date + hour, or 2/ match other constellations around NCP (such as Ursa Minor/Major and Cassiopeia).

Otherwise you may be up to 2x40' (1.33°) offset from NCP, and that might explain your trouble.

Thanks. That makes sense now, doh!!  

[bobro]

Here's Mr Pelican looking a bit less blue - tried out (in GIMP) decomposing an image to separate RGB layers for the first time, allowing the blue haze to be adjusted out. Quite a useful feature.

[Peco4321]

On 29/06/2017 at 12:30, rotatux said:

Not enough: you have to rotate the polar scope to either 1/ match your local longitude + date + hour, or 2/ match other constellations around NCP (such as Ursa Minor/Major and Cassiopeia).

Otherwise you may be up to 2x40' (1.33°) offset from NCP, and that might explain your trouble.

Just messing and if I do this, unscrewing the polar scope to rotate a bit to match up with the constellations makes it wobble quite a bit, surely that is loosing the polar scopes alignment. Or am I missing the point. 

[Peco4321]

On 29/06/2017 at 12:30, rotatux said:

Not enough: you have to rotate the polar scope to either 1/ match your local longitude + date + hour, or 2/ match other constellations around NCP (such as Ursa Minor/Major and Cassiopeia).

Otherwise you may be up to 2x40' (1.33°) offset from NCP, and that might explain your trouble.

Just messing and if I do this, unscrewing the polar scope to rotate a bit to match up with the constellations makes it wobble quite a bit, surely that is loosing the polar scopes alignment. Or am I missing the point. 

IMG_3390.MOV

[Stub Mandrel]

Just studied my GOTO box code in detail. Discovered the 'guiding' routine I thought I'd have to remove and re-write is actually OK!

I just have to figure out which button is which wire... but I'll be trying to break the EQ3 sub-length record soon

 

[alacant]

2 hours ago, Peco4321 said:

unscrewing the polar scope to rotate a bit to match up with the constellations makes it wobble quite a bit

Hi. No. Leave the polarscope tight. Rotate the RA axis to the 6 o'clock position. That is when Polaris is at the top of it's orbit. Clamp RA. Now rotate the RA scale to whatever time Polaris transits. E.g. today at Alicante,  

 Polaris                                       
     
                                      alicante                                       
                  Location:  W  0°38'00.0", N38°00'00.0",     0m                   
                     (Longitude referred to Greenwich meridian)                      
     
                        Time Zone:  2h 00m east of Greenwich                         
     
      Date               Rise  Az.       Transit Alt.
     (Zone)                                                                  
                          h  m   °         h  m  °          
2017 Jul 01 (Sat)        ***** ***        10:17 39N        

Then, when you're ready to align, rotate the RA to the current time and adjust alt-az to put Polaris in the small circle when looking through the guidescope **EDIT: polarscope. HTH.

Edited July 1, 2017 by alacant

[bobro]

51 minutes ago, Stub Mandrel said:

I'll be trying to break the EQ3 sub-length record soon

Another Stub sub challenge to us all?  

[Peco4321]

4 hours ago, alacant said:

today at Alicante,  

I wish, sure it's better than East Yorkshire ?

Thanks for this, next clear night will give it a go.