Sunday, March 31, 2013

Gull to Thor Widefield

Gull to Thor Widefield by S Migol
Gull to Thor Widefield, a photo by S Migol on Flickr.
Via Flickr:
Gull to Thor Widefield as seen in the backyard. Used a Pentax SMC TAKUMAR/6x7 1:4/200mm lens with adapter to fit the Pentax K10D camera. IDAS LPS P2 filter on the lens with a Baader Ha filter inside the adapter. This was required because the camera is a full-spectrum modifed one and there was sigificant unfocused light from the lens.

This is a stack of six 1200 second subs that had been calibrated with Maxim and stacked in Pix Insight.

My first effort with a monochrome image, it's a pretty grungy one. In the process of working on the file, I resampled to 50% to remove evidence of bayer lines due to the lower resolution of the red channel.

This turned out better than I'd expected, given the conditions. I'm glad that I tried it. I'll give it a try again another time, but with a non-converted camera or add an IR filter in the mix.

Here's the platesolve from PI:
Referentiation Matrix (Gnomonic projection = Matrix * Coords[x,y]):
-0.003476522382 -0.000033246131 +3.384950874320
+0.000028792576 -0.003478460023 +2.208816745728
+0.000000000000 +0.000000000000 +1.000000000000
Resolution ........ 12.519 arcsec/pix
Rotation .......... 0.495 deg
Focal ............. 100.01 mm
Pixel size ........ 6.07 um
Field of view ..... 6d 43' 45.2" x 4d 28' 20.0"
Image center ...... RA: 07 09 26.127 Dec: -11 48 38.53
Image bounds:
top-left ....... RA: 07 23 08.458 Dec: -09 35 10.16
top-right ...... RA: 06 55 54.322 Dec: -09 31 51.77
bottom-left .... RA: 07 23 11.430 Dec: -14 02 58.90
bottom-right ... RA: 06 55 30.463 Dec: -13 59 36.75

Tuesday, March 19, 2013

Siamese Twins Galaxies

Siamese Twins Galaxies by S Migol
Siamese Twins Galaxies, a photo by S Migol on Flickr.
Via Flickr:
The Siamese Twins Galaxies, NGC 4567 and NGC 4568.

These two galaxies are part of the Virgo cluster and are about 60 million light years distant.

Taken over a series of three nights at home. I only used two nights of data as the third night was so far off center and it only had an hour's worth of subs that it wasn't worth using.

Taken with the modified Pentax K10D camera running at an EXIF temp of 9-11C (TEC set to -5C). Used the Orion 127mm Maksutov Cassegrain scope. Tracking was hard to nail down over the sessions as the air turbulence was making a challenge. I had a struggle keeping the RMS at 1 arcsecond, which was above the resolution of this setup. Thus, all details are blurred. I think that much of this lies at the use of the Orion ST80 as a guide scope with a poor quality IR filter. The guide star images didn't have good centroids.

Guided and calibrated with Maxim using 12 darks, 64 bias, and 16 flats and hot pixel map.
Registered and Stacked using PI as DSS couldn't detect the faint stars remaining after calibration.
Rest of the processing in PI used masked stretch, DBE, A trous wavelet processing (including a large scale flattening effort to smooth out some odd rings).

There is a fair amount of detail, but this is limited because of the guiding issues. I'm not sure that I'll have a chance to return to this target before the end of the month.

The reason why I selected this target was because I'd "won" the Cloudy Nights competion with the Jellyfish Nebula picture from two months ago. I thought that all the SCT owners would jump at the chance to image something like this target.

Here's the PI-generated plate solve:
Referentiation Matrix (Gnomonic projection = Matrix * Coords[x,y]):
+0.000000503647 +0.000228108926 -0.246675434483
-0.000228060582 +0.000000327102 +0.349607831977
+0.000000000000 +0.000000000000 +1.000000000000
Resolution ........ 0.821 arcsec/pix
Rotation .......... -90.110 deg
Focal ............. 1524.81 mm
Pixel size ........ 6.07 um
Field of view ..... 41' 60.0" x 29' 30.3"
Image center ...... RA: 12 36 36.612 Dec: +11 14 02.27
Image bounds:
top-left ....... RA: 12 35 36.181 Dec: +11 35 00.44
top-right ...... RA: 12 35 36.705 Dec: +10 53 00.80
bottom-left .... RA: 12 37 36.664 Dec: +11 35 02.99
bottom-right ... RA: 12 37 36.897 Dec: +10 53 03.33

Wednesday, March 13, 2013

Widefield is hard

Now I know why people don't use camera lenses a lot...

The image here is taken with my modified camera with a 165mm medium format lens.

It's nothing more than the STF from PixInsight of the stack after calibration and integration.  The cause of the red halos around the stars is unfocused near IR light.  Thus, the lens blurs the star images.  I was using the IDAS LPR filter with the setup and so this is part of the reason why the red shows up.

I will be trying one more shot at this image and not worry about getting full color.  Instead, I'm just going to use the Ha filter that I have.  I'll try it with the IDAS filter as well as without it.

I'm thinking that with the filter in place, I will see uniform performance of the lens across the field.

I'm also going to step up to the 200mm lens now that I found a way to rotate the camera on the support.

Friday, March 8, 2013

Revisiting RAW

There was a recent post on the Pentaxforums where a new user of the K5IIs was studying noise profiles.  It seems that Pentax was doing something similar as Canon does when measuring black levels and then skewing this before writing the RAW file.

It got me thinking about how the K10D performs on this as well.

Wednesday, March 6, 2013

Cleaning Objectives

I've had my SV4 for several years, since 2004.  It spent most of the early time going in and out of the case, sometimes right after observing.  Most of the time it was dry when put away.

Late in 2012, I was aware of some severe dewing issues when observing in the back yard.  There were problems with bad connections on the dew heaters (which have been solved by use of hot melt glue).  One particularly bad morning, I saw that there was dew forming behind the objective!

On that day, I also saw that the SV70ED had dew that appeared to be inside, between the elements.  This was not good.

At that time, I figured out what to do about the dew heaters and I also started a practice of putting silica gel sachet packs just inside the caps.  This has dried out the scope nicely and kept things clear.

I was still worried about the apparent dewing on the inside of the tube and how it showed some dust motes that had spread a little over time.  Fearing fungus, I wanted to find a way to clean the inside of the scope.

Cleaning the inside of the SV70ED was easy and I was able to do it with a microfiber cloth once I'd unscrewed the scope tube from the focuser.

It wasn't until Vic posted on the yahoo group here the procedure to disassemble the larger scope body that I felt confident enough to open the SV4.  Once I read this post, I knew enough to do it.

I removed the scope from the rings and clamps (a chore in itself) and then pushed the dew shield back.  The lens cell was a little stiff to open, but once I got it started, it just spun off.  There are heavy pipe threads on the cell, so there's little chance to cross them.  I dabbed a microfiber cloth with some methanol and wiped the inside of the glass after using the puffer.

Now the inside of the cell is as clean as I can get it.  There are a few marks where debris had sat on the glass for a long time, leaving a defect in the multi-coating.  At least the glass is clean and there will be less opportunity for fungus to start.

I also noted that the focuser was loose on the scope tube.  Probably because of my struggles with clamping and binding causing a torque on it.  It's now tight.

No pictures of the procedure.

Also during this time I put a nylon 1/4-20 thumbscrew on the camera to thermally isolate it a bit more.  

Reducer Flattener Testing

I've been on a quest to find a well-matched reducer/flattener combo for my SV4.

This scope is a F6.41 fl 655mm 102mm diameter apo, LOMO triplet with OK4 glass.  It's a rareish beast in that it falls between the short astrographs and long triplets.  

It's already pretty well corrected and the SSF6 flattener does a good job of controlling the star images out to the edges of the field on an APS-C sensor.  I've always wanted a little bit more, though.

So, everytime I can see a new reducer design available in my price point, I try it out.

  • I've tried the Televue TRF 2008 - with ugly results.
  • I've tried the WO Type II - also with ugly results, although not as bad as the TV.
  • I've also tried the Astronomics one for ED F6 scope - and this has been the best so far.
  • I recently tried the WO Type 6 for F6 scopes.  It also is not so good.