Strange DSI PRO

[Aster]

Last night I did some imaging with the old 8" F5.6 Newt and the DSI Pro with IR Filter unguided on EQ6 mount.

Used Meade Envisage Drizzle, dark subtracted, tiff, save all images.

This morning having a look at the results I found that I had different size images, like the image format changed during exposure.

Anyone, who has a DSI Pro, has had that happen to them.?

Attached some images so you can see what I mean.

Tarantula 30sec exposures 10 stacked in registack, de-interlaced in Photoshop, autolevel adjust.

Tarantula 30sec 1 exposure raw tiff image from the same run.

Tuc47 - 2 - 15sec x1 just de-interlaced.

Tuc47 - 15sec. x 1 raw tiff image.

[citivolus]

I've never used "drizzle", but it up samples the image, which could explain your sub frame size difference. Did you change your "Drizzle Resolution" under Drizzle Settings at any time?

[Dr Nick]

If you changed the drizzle settings it may cause the image's size to change like what has happened here. I think it may also be caused by the way that you have envisage set to stack the frames ;)

[Lee]

I think if you have any drift between subframes you can get slightly different stacked frame sizes - and I'm sure drizzle increases the size of the final image too....

[Aster]

Nope, as this actually was my first serious try I left everything at the default settings.

[Aster]

Used the default settings for drizzle in Envisage.

Used Registack to stack the images, multipoint.

[Aster]

Hmmmm, don't know about that, but will invetigate that part furhter

[dcalleja]

Hi
I presume if you didn't use the Drizzle Resolution or Extended View features (which would have definitely changed the scale) that you used the derotate feature (all other Drizzle settings at 1.00)? ie: select Drizzle then select two stars (ends up with a line drawn between them). I use this because my scope is Alt Az but I let Envisage stack for me as I've had no joy with registax doing it after the fact.

I'm not sure if the scale changes between images (should not) but the position definitely does (due to rotation) and I've had a lot of trouble registering my RGB-Envisage stacked composities after using drizzle.

Not sure if this helps but I've read that selection of the two stars is important - they should be in the middle third of the screen not at the edges.

[[1ponders]]

If the Drizzle feature is anything like the SBIGs Track and Accumulate then yes you will get different sized images depending on how long you allow the capture process to go on.

[[1ponders]]

He is an example of what I mean
The first shot is 30shots at 30 sec T&A but autoguided. The second shot is 64 shots at 10 sec T&A without autoguiding.

[Ric]

Hi Aster, I don't know if this may help or not but I was told on another forum that when using Drizzle if the settings are all set to 1.00 then it will have the effect of disabling Drizzle. I usually image in fits3p.

I was advised to use the settings of

Drizzle Resolution 1.00
Extended View 1.50 to 1.70 (dont go below 1.20)
Pixel fraction 1.00

I agree with Dan try to avoid stars around the edges.

Hope this helps

[Aster]

Have had another go with drizzle and will give it a miss for the time being until such time I gain a bit more experience. Posted a couple of other shots taken with Envisage Deep Sky.

Dan,

Yes, I used derotate by selecting 2 starts although I have a EQ6 Mount.

Paul,

Had no idea that as you start to accumilate more images under drizzle that your image size would change

Ric,

Extende View, so I was told, under drizzle in Envisage does only work with a Meade Mount and autoguiding.

[[1ponders]]

It may not, but it makes sense to me and the only experience I've had with anything similar is the T&A

[Ric]

I didn't realise that Aster, sorry if I've led you astray.

Cheers :)

[peter_4059]

I thought the Drizzle function only worked with Meade mounts. I got the impression it moved the mount to get a larger scale picture. Here's the description from the DSI manual:

Developed by NASA for the Hubble Space Telescope, Drizzle has features that dramatically increase the resolution and field of view of the Deep Sky Imager Pro's CCD chip. When the object being imaged would normally need a bigger chip camera, the astrophotographer can enable the Drizzle feature, which produces an effective 4.9 mega pixel camera from the Deep Sky Imager Pro's 640x480 CCD chip with Meade AutoStar controlled telescopes.
It may seem that we are exaggerating, so here are the numbers: If a user selects Drizzle and inputs the value of 2 in the Drizzle 'Extended View' setting (effectively making a 2x2 mosaic), and a value of 2 in the 'Drizzle
Resolution' (which takes multiple undersampled dithered shots of the object and reconstructs the image at higher resolution), they will end up with a picture that is 2560 pixels by 1920 pixels or 4,915,200 pixels. The uncompressed RAM file (in FITS format) will be approximately 10 megabytes. Drizzle is not simply enlarging the image as in interpolation.We move the telescope which in turn moves the image across the CCD sensor to perform
seamless precision mosaics.