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Photometric V filter sources?

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#1 petemumbower

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Posted 19 June 2012 - 10:41 AM

I am starting to lose my drive for doing "pretty pictures" and always wanted to get into photometry. Doing research online via AAVSO and few books, I know I need at least a V filter to be able to contribute to the AAVSO database. I use a ST-7E NABG for my CCD and would use the CFW with 1.25" filters. But what I am having a hard time with is a source for a relatively low cost V filter. The only place I have found currently is Astrodon and it seems that will be around $175. I do remember seeing those size V filters in the past for less than $100. Or is Astrodon the only game in town? Those filters do seem to be quite rare on Astromart, so going the used route seems to be a lucky shot.

#2 NJScope

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Posted 19 June 2012 - 02:12 PM

Pete:

The older Schuler filters were closer to $100 but it would appear that Astrodon is the only viable option if you want one now. SBIG sources their UBVRI filters from Custom Scientific. I checked the OPT website and they do have a selection of Custom research filters on sale ($150) but the V-band ones are back-ordered. FWIW be prepared to wait since it took 4 months for Custom to deliver a 1.25 photometric clear filter for my CFW9.

#3 petemumbower

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Posted 19 June 2012 - 02:36 PM

Kevin,

Thanks for confirming my thoughts on a V filter source. Guess I will have to put up the $$$ to get one if I want to start this summer. Though, I will give OPT a call and see if they have a lead time for CS V filter.

One other thought I had was going into the Sloan filters. Is there many amateurs using them? Of course that will cost me more. But if that is the direction photometry is going, I might as well go with it now instead of down the road. Does that make sense?

#4 groz

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Posted 19 June 2012 - 05:28 PM

There are two parts the the equations.

1) Getting the process down pat, and, gathering data
2) Submitting data to various database(s).

For the first part, you dont need a V filter, use what you have, get some practise in taking shots, then reducing them for photometry. For some programs, clear or 'no filter' are desireable. For some, the specific filter in use, is not really important, as long as it's the SAME filter through the series.

A good example, you can do exoplanet transit measurements, and submit into the ETD using any filter you like, choose what works best for your gear / location. Consistent measurements, with accurate timing are the important keys for a transit series.

The V filter really only becomes necessary if you want to submit data to a database which is trying to 'level' the observations from various sources, and the BVR filter set is the traditional 'leveller'.

FYI, over a period of a few months, I was able to pick up one V, and one BVR set from amart, for substantially less than the going rate for brand new filters. I wasn't in a rush tho, because we got the first BVRI set on a blowout, for a good price, then waited patiently to find the right filters for the other telescopes, when they showed up for a good price. We still have the L, but have replaced the RGB with BVR on both of our kits now.

#5 gavinm

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Posted 19 June 2012 - 06:43 PM

Arne Hendon gave me a V filter a few years ago, which was nice, but I've only used it about 5 times tops. So that means they must be cheap somewhere.

I use SLOAN filters for my photometry, based on the recommendations of experts. Mainly for calibrations and star field measurements and occasionally light curves of specific targets when someone asks...

BUT my main filter is a CBB (broad band blue block filter) which I would use for general photometry, about 90% of the time.

#6 NJScope

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Posted 19 June 2012 - 08:53 PM

Peter:

I would not recommend spending money on a Sloan photometry set until you have given photometry a try for a while. As others have said, get the basics down first. Minor planet light curves are usually captured with a clear filter so they are a good first target to get your feet wet.

#7 petemumbower

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Posted 20 June 2012 - 08:01 AM

Thanks everyone for the advice. It was clear last night so I did a practice run with TV Bootis, a RR Lyrae that was right on the meridian when it got dark enough out. I went to the AAVSO site to find this star and generated a finder map. I took a series over a 2 hour period with darks, bias, flats, flat darks afterwards (C9.25-FR-ST7E-no filter). Overall the data collection went pretty smooth. I was able to find the field and get a run setup in MaximDL pretty easy. Then I slept for a couple of hours. Now I need to process the data.

What program is recommended for that? I do have MaximDL, which seems to be the only one that does photometry. But is there any other software worth considering?

It is looking to be clear tonight also, so I will be looking for another practice target. Man is this fun and exciting!

#8 brianb11213

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Posted 20 June 2012 - 10:38 AM

I do have MaximDL, which seems to be the only one that does photometry. But is there any other software worth considering?

If you have Maxim, and know how to use it, that sounds like A Good Plan ™.

I've used the photometry functions in AIP4WIN v2 ... I have a copy, it works and I understand what I'm doing with it.

#9 groz

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Posted 20 June 2012 - 01:38 PM

Thanks everyone for the advice. It was clear last night so I did a practice run with TV Bootis


I have used gsc 3074-0114 a number of times for testing out various configurations. It is listed as mag 13.8 in the gsc catalog, but gives roughly a 0.8 mag swing over a period of a couple hours. It's fairly well situated at this time of year, and generates a very nice plot.

If you are looking for a starter target, that gives nice 'instant gratification' when you generate a plot from the data, this one does the job nicely.

#10 petemumbower

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Posted 20 June 2012 - 03:42 PM

groz, thanks for that variable star, it is going to be clear tonight again and I will do a run with it.

#11 btieman

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Posted 20 June 2012 - 06:47 PM

Http://www.aavso.org/vsx/index.php

Great site where you can search the variable star database for period, magnitude, etc...

#12 petemumbower

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Posted 20 June 2012 - 07:11 PM

btieman- Thanks for the link, that is now bookmarked and will be used frequently!

#13 petemumbower

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Posted 20 June 2012 - 07:14 PM

Well I got home and after getting the kids to bed was able to process my data from last night and generated a light curve in MaximDL. This was a very easy process and I am really happy with my results. Below is a snapshot of my efforts.

Attached Files



#14 rutherfordt

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Posted 20 June 2012 - 08:51 PM

Pete:

The AAVSO will accept data taken through a green photographic filter-- select "tri-color green" for the filter used when you submit your data.

Tom

#15 NJScope

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Posted 22 June 2012 - 09:45 PM

Peter

That's a pretty good start! Good luck with the rest of the curve. What software are you planning to use to phase all of the light curve data when you are finished? I've found MPO Canopus to be very useful for converting images to catalog-based magnitudes and period solving. Just a minor nitpick...by convention the y-axis in your figure should be reversed with the brightest values on top.

#16 petemumbower

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Posted 23 June 2012 - 08:03 AM

Kevin, thanks! Being new photometry I am still learning a lot, but thanks for the y-axis heads up, I over looked that. Also, I was wondering how to sync up curves that a days or weeks apart. I only have MaximDL for reducing the data and Excel at this point.

#17 Ed Wiley

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Posted 23 June 2012 - 04:48 PM

There are variable observing programs that do not require a V-filter, as mentioned in previous posts. However, for most AAVSO submissions (not all!), the minimum requirement is a V-filter. One problem with used Schuler Vs is that they frequently have white crud around the margins (and perhaps on the center) that has to be cleaned off (as mine did). So if you are buying used, ask first or plan on doing some delicate cleaning if you see the white stuff. I don't have them, but apparently the other Schuler photometric filters do not suffer from this.

Many programs do great data reduction. Since I am an AAVSO member, I take advantage of VPHOT which is on-line and very slick for many photometric reduction tasks. I assume you have downloaded the latest AAVSO CCD manual.

Good measures, Ed

#18 petemumbower

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Posted 24 June 2012 - 08:38 AM

ED, thank you for the info on used Schuler V filters. I had heard about "fogging" with these older filters and the white crud must be it. I suppose I should just bite the bullet and purchase a new one from Astrodon. I am really enjoying doing this and can see myself doing photometry for many, many years to come.

I do have the latest AAVSO CCD manual and have been through it once. I was just starting to go through it again to refresh my memory on things. Also, I think joining the AAVSO is going to be well worth it.

#19 Ed Wiley

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Posted 24 June 2012 - 07:23 PM

Glad to help, Pete. The Astrodons last for many years. For my part, I bought a ST403ME with the BVI internal filter wheel, which works great. But if I had an ST7 and a filter wheel I would go the Astrodon route. You can add filters as you get into the photometry deeper. Many observers are happy only with the V.

Good measures, Ed

#20 gavinm

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Posted 24 June 2012 - 08:08 PM

The filter crystalisation is not an 'old' filter problem, but a 'cheap' filter problem. Due to the type of glass substrate being exposed to the air, more expensive filters have dielectric coatings (or similar) that obviously push up the price.

Mine is the cheaper AAVSO version which does suffer from this, but it cleans off easily.

#21 Ed Wiley

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Posted 25 June 2012 - 07:45 PM

Hi Gavin: What method did you used to clean your filters, I suspect many on the forum would like to know.

Ed

#22 gavinm

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Posted 25 June 2012 - 11:17 PM

Will probably sound like sacrilege but I just use a lens cloth (on the V-filter). I have never cleaned my other photometric filters. I kept them pretty clean installing them and I am pretty pedantic about dust around the camera.

#23 Ed Wiley

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Posted 27 June 2012 - 07:17 PM

No sacrilege to my mind, Gavin. Thanks for sharing. I have heard everything from toothpaste to find abrasive.

Ed

#24 Tim Hager

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Posted 04 July 2012 - 03:17 PM

I've cleaned my Schuler V filter with a finger dipped in water and then a little red mirror polishing rouge left over from an old mirror kit. Then a rinse. I suppose cerium oxide will work too.

Incidentally, the B filter suffers from this problem too. The type of glass used in the B and V Schuler filters reacts with moisture in the air to form a coating which is easily washed or polished off.

...Tim

#25 Ed Wiley

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Posted 08 July 2012 - 08:56 PM

Thanks, Tim: I think that is what Arne Henden also uses. Toothpaste for me.

Ed






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