NGC 7331 dithered !

[numchuck]

I'm slowly learning all of this . Weather and work get in the way ; and last Wednesday was only my 4th night out this year . Taken with QHY183 on ES127 fcd 100 , this image consists of 267 eight second frames with gain of 24 and offset of 20 (only 35 minutes) I had 3 other stacks totaling two and a half hours in all ; but I had trouble with my FWHM focus scores in SharpCapPro and so I kept "upping" the limit ; but my data suffered for it . Anyway , I did my guiding with PHD2 and dithered for the very first time (every 2 minutes) . I don't know yet what all of the optimum settings should be ; but I'm slowly learning what NOT to do . I also added 40 dark frames to the stack . Thanks to you all for your help , and especially to you , Robin

[turfpit]

Well done - keep at it.

I found my progress was long periods of the same and then small insights that enabled big leaps.

Weather and work get in the way

Solved the work one - retirement, no solution yet for the weather

Dave

[BlackWikkett]

Congratz! Nice image, even illumination and round stars to the edges. Keep at and don't be afraid to experiment.

[numchuck]

Thank you both . I was very happy that Robin added all of the PHD2 guiding features . I always take dark frames but I don't yet have a setup for taking flats at night ; but the dithering really helped a lot . I'm thinking now that a focus stepper motor might help me to keep up with the changes in FWHM scores .

[BlackWikkett]

For flats I use this tracing tablet and a t-shirt. Put the tablet at lowest setting and the t-shirt one layer stretch over the end of the OTA with the tracing tablet resting on top while the OTA is pointing at the zenith.

https://www.amazon.com/gp/product/B01M2 ... UTF8&psc=1

That is the US Amazon link, if you're outside of US this should redirect for you.

[numchuck]

Thanks Wikkett ! !

[turfpit]

The panel solution suggested by Wickett is a good one as it is a single, cost effective solution for those with multi scopes of varying apertures.

For flats I have, for a year or so, been building my own flat panels which consist of:

• plasticard sheets

• electro luminescant panel

• inverter

• battery power

Plasticard is light, durable and easy to work with simple tools.

This is my Mark 1, 2 pieces of card plus EL panel plus 2 pieces of plastic rod Gorilla glued onto the card. Runs off 3V = 2x1.5V batteries.

MK1.JPG (46.88 KiB) Viewed 2631 times

I have trouble with wind in my part of the world. A Mark 1 got lifted off the scope and did not fare well on landing. Enter Mark2 which fits securely over the end of the telescope. Runs off 12V = 8x1.5V batteries. approximate cost £30 with an A6 EL panel.

MK2.JPG (87.05 KiB) Viewed 2631 times

This is card, EL panel, card (with hole the size of the scope aperture), standoff pillars, card (with hole to fit over scope tube).

With the 12V panel, I ran into brightness issues with 2x2 binned flats - hence the sacrifice of a white teeshirt to kill the light.

teeshirt-sacrifice.JPG (75.81 KiB) Viewed 2631 times

I am building another 3V light panel which will work for the binned flats. These are the parts, approximate cost £20 with a 100mm EL panel:

MK2-parts.JPG (83.54 KiB) Viewed 2631 times

Parts list:
https://www.ebay.co.uk/itm/1-1-5-2-3mm- ... 2749.l2649

https://www.ebay.co.uk/itm/10cm-EL-Pane ... 2749.l2649

https://www.ebay.co.uk/itm/Basic-Driver ... 2749.l2649

A source for EL panels:
https://www.earlsmann.co.uk/lighting-co ... l-panels/


I have done this with the C8 - works but is a 'next day' type of solution and would not be practical if having to go to work.

C8-flats.JPG (91.28 KiB) Viewed 2631 times

The EL panel for the C8, 250mm x 250mm, cost ~£45.


There are some commercial solutions search for 'pegasus flat panel' or 'lacerta flat panel'. One solution is 255 brightness levels, software controlled over USB bus.

Also Brian (@oopfan) has developed his automated 'flatinator' solution.

For completeness I manage my flats exposures using the histogram, keeping to around 50%. I use RAW so no need to worry about colour balance as that gets sorted later. The mono flat has only the single curve.

colour-flat.JPG (59.66 KiB) Viewed 2631 times

mono-flat.JPG (58.79 KiB) Viewed 2631 times

My Mark 2 works well for my situation, portable and gusty wind resilient. The EL panel vendor now offers a plunger switch with 1m lead which is better than the switch on the back of the scope.

[Note: I don't use rechargeable batteries as they don't quite make the voltage that the inverters require]

Dave

[numchuck]

Dave , that helps a lot . When I adjust everything to get to the 50% histogram , can I set the black level where ever I want , or does it need to stay at the same setting as what my astrophoto requires?

[turfpit]

I keep the settings such as gain and black_level the same.
Take lights
Take darks, same settings as light
Take bias, adjust only exposure to minimum setting
Take flats, adjust only exposure to get 50% histogram

That strategy seems to give me reasonable & consistent results with a CMOS camera.

With my Atik CCD there is only exposure available.

[numchuck]

I like the simplicity of that (I just took a screenshot of your reply to save for reference) The subject of calibration frames is still somewhat mysterious to me . I've been reading posts on CloudyNights forums ; but usually calibration frames are spoken of "matter-of-factly" ; so for me , the conversation has been like , coming in to a theater , when the show is half over . Thanks very much , Dave ,for your answer