[Aavso-photometry] V filter only - transforms possible?

[Jim Jones]

Sure it's possible.  See Henden's  "The M67 Unfiltered Photometry
Experiment" in JAAVSO Vol 29, 2000.

With some encouragement from Arne a couple of years ago, I found my V
transform with fairly good results.  The problem is using the transform
without reliable B-V data for both stars.

Jim Jones

Michael Newberry wrote:
> No, not possible.
>
> Michael Newberry
>
> ----- Original Message ----- From: "Tom Krajci" <tom_krajci at tularosa.net>
> To: <aavso-photometry at aavso.org>
> Sent: Thursday, December 18, 2008 3:48 PM
> Subject: [Aavso-photometry] V filter only - transforms possible?
>
>
>> I have a CCD/scope rig with only a V filter screwed into the CCD 
>> nosepiece. No filter wheel, no other filters.
>>
>> Here's the $64 question.  Is it possible to determine transformation 
>> coefficients for this setup with only a V filter?
>>
>> If I do differential photometry of a Henden calibrated field (V 
>> magnitudes and color indices are known for the comps, *and* the 
>> target), can I transform to V magnitudes?
>>
>> What if I take images of ye-olde standard field, M67, and compare my 
>> instrumental magnitudes with the catalog magnitudes?  What sort of 
>> correlation/transformation coefficient will that give me?  (If it's 
>> not a true transformation coefficient, then what is it called - a 
>> pseudo transform?)
>>
>> (I know that if I use this V-filter-only rig on uncalibrated comps 
>> and targets, i.e. V mags and color indices are unknown,...then there 
>> is no way I can transform.  Therefore I'm looking for 'easy' target 
>> fields that I can work to higher precision...hopefully with a proper 
>> transform to V magnitudes.)
>>
>> I'm just trying to get the most out of this V-filter-only system.  
>> (And if I can't transform to V with this setup...how close can I 
>> get?  How do I report the magnitudes?...as untransformed?)  (And if I 
>> can't transform to V with this setup...what do I need to acquire?...a 
>> B or R filter?)
>>
>> Thanks in advance.
>>
>> -- 
>> -------------------------------------------
>> Tom Krajci
>> Cloudcroft, New Mexico
>> http://picasaweb.google.com/tom.krajci
>>
>> Center for Backyard Astrophysics (CBA)
>> http://cbastro.org/ CBA New Mexico
>>
>> American Association of Variable Star
>> Observers (AAVSO): KTC http://www.aavso.org/
>> -------------------------------------------
>>
>>
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