Internal Cut Filter Transmission

emil1 · 09-24-2020, 01:15 AM

Hi,

Firstly I want like to say hello. I'm happy to be a part of such a great community so much interesting questions and suggestion to our k70

I'm thinking about using my camera to astrophotography and buy some tracking mount to able make a long exposures. But firstly I would like to know how much wavelenght I lose because of internal cut filter inside k70. I don't want to make any modification for now. So, my question is anyone know what exactly is the spectrum of wavelenght? The best will be to see a chart..

**ProfessorBuzz** · 09-24-2020, 05:39 AM

Put a diffraction grating in front of a halogen lamp, and shoot the spectrum. It will give you some idea of the blocking. Or go shoot the North America Nebula NGC7000 which is huge and bright in Hydrogen Alpha.
Otherwise someone needs to disassemble the K70 and send the IR blocking filter to be professionally analyzed, and then you need the datasheet for the QE curve of the K70 sensor.

**MossyRocks** · 09-24-2020, 06:12 AM

Over in the astro group I have seen a number of people state that even the unmodified pentax cameras are fairly sensitive to the Ha spectrum. As far as other wavelengths lost I don't know but pentax cameras a very capable astro cameras. I know you can get them astromodified so they let more of the IR range in. I would suggest going and asking over in the astro group and someone will likely have all the info you need or be able to point you to it.

**Bob 256** · 09-24-2020, 08:36 AM

I don't know if it will help but in post #5 I posted the transmission of the K-1 UV/IR cutoff filter. It could be that the K70 is similar??
Transmission does fall off on the red end so removing such a filter might be advantageous but not absolutely necessary, and it will also depend on the sensitivity of your sensor at the hydrogen alpha wavelength (656nm).

UV/Haze filters - PentaxForums.com

**AstroDave** · 09-24-2020, 09:52 AM

This site shows a bunch of filter curves, including for a few (older) Pentaxes: Internal Cut Filter Transmission - Kolari Vision

**Apet-Sure** · 09-24-2020, 10:01 AM

Welcome to the forum. Very nice to have you with us.

emil1 · 09-24-2020, 12:26 PM

Thank you for so match responses!

I saw before chart for K-01, looks very good. It will be good if K70 has the same cut-off params. Also I saw charts from kolarivision.com and have the same thoughts, it will be good if k70 will be simillar to k10D. But still I'm not sure how it's look like truly on k70.
It's a good idea to ask about some images from k70 on astro group. It will give a some point of view

emil1 · 09-24-2020, 12:32 PM

Ohh.. I need to be a group member to create a new thread..
There is a possibility to add yourself there?

**bwgv001** · 09-24-2020, 01:27 PM

Maybe these guys are a good source fort he information you are looking for.
clip_filter_for_pentax_k1

emil1 · 09-25-2020, 01:11 AM

Good idea! I asked them if there is a sense to use Ha filter with non modified camera

09-24-2020, 01:15 AM	#1
emil1 New Member Join Date: Sep 2020 Posts: 7	Internal Cut Filter Transmission Hi, Firstly I want like to say hello. I'm happy to be a part of such a great community so much interesting questions and suggestion to our k70 I'm thinking about using my camera to astrophotography and buy some tracking mount to able make a long exposures. But firstly I would like to know how much wavelenght I lose because of internal cut filter inside k70. I don't want to make any modification for now. So, my question is anyone know what exactly is the spectrum of wavelenght? The best will be to see a chart..

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09-24-2020, 05:39 AM	#2
ProfessorBuzz Loyal Site Supporter Join Date: Feb 2018 Posts: 1,903	Put a diffraction grating in front of a halogen lamp, and shoot the spectrum. It will give you some idea of the blocking. Or go shoot the North America Nebula NGC7000 which is huge and bright in Hydrogen Alpha. Otherwise someone needs to disassemble the K70 and send the IR blocking filter to be professionally analyzed, and then you need the datasheet for the QE curve of the K70 sensor.

09-24-2020, 06:12 AM	#3
MossyRocks Loyal Site Supporter Join Date: Nov 2017 Location: Minnesota Photos: Gallery \| Albums Posts: 2,982	Over in the astro group I have seen a number of people state that even the unmodified pentax cameras are fairly sensitive to the Ha spectrum. As far as other wavelengths lost I don't know but pentax cameras a very capable astro cameras. I know you can get them astromodified so they let more of the IR range in. I would suggest going and asking over in the astro group and someone will likely have all the info you need or be able to point you to it.

09-24-2020, 08:36 AM	#4
Bob 256 Site Supporter Join Date: Jun 2008 Location: Idaho Photos: Gallery Posts: 2,375	I don't know if it will help but in post #5 I posted the transmission of the K-1 UV/IR cutoff filter. It could be that the K70 is similar?? Transmission does fall off on the red end so removing such a filter might be advantageous but not absolutely necessary, and it will also depend on the sensitivity of your sensor at the hydrogen alpha wavelength (656nm). UV/Haze filters - PentaxForums.com

09-24-2020, 09:52 AM	#5
AstroDave Loyal Site Supporter Join Date: May 2007 Location: Flagstaff, Arizona Posts: 1,637	This site shows a bunch of filter curves, including for a few (older) Pentaxes: Internal Cut Filter Transmission - Kolari Vision

09-24-2020, 10:01 AM	#6
Apet-Sure Site Supporter Join Date: Dec 2015 Location: Goldsboro North Carolina Photos: Gallery \| Albums Posts: 2,861	Welcome to the forum. Very nice to have you with us.

09-24-2020, 12:26 PM	#7
emil1 New Member Join Date: Sep 2020 Posts: 7 Original Poster	Thank you for so match responses! I saw before chart for K-01, looks very good. It will be good if K70 has the same cut-off params. Also I saw charts from kolarivision.com and have the same thoughts, it will be good if k70 will be simillar to k10D. But still I'm not sure how it's look like truly on k70. It's a good idea to ask about some images from k70 on astro group. It will give a some point of view

09-24-2020, 12:32 PM	#8
emil1 New Member Join Date: Sep 2020 Posts: 7 Original Poster	Ohh.. I need to be a group member to create a new thread.. There is a possibility to add yourself there?

09-24-2020, 01:27 PM	#9
bwgv001 Site Supporter Join Date: Aug 2015 Location: Alabama Photos: Gallery Posts: 697	Maybe these guys are a good source fort he information you are looking for. clip_filter_for_pentax_k1

09-25-2020, 01:11 AM	#10
emil1 New Member Join Date: Sep 2020 Posts: 7 Original Poster	Good idea! I asked them if there is a sense to use Ha filter with non modified camera