Manually Focusing on Stars with Standard K-3 18-135mm lens

**GUB** · 05-12-2021, 05:33 AM

An astronomer mentioned this technique tonight at our camera club meeting.
Has anyone used the bahtinov filter.?
They are available https://www.aliexpress.com/af/bahtinov-focusing.html?d=y&origin=n&SearchText...20210512042112

Attached Images

damianc · 05-12-2021, 05:46 AM

I can only speak for their use on a 400mm astrograph where they are brilliant. I'd note the caveats at the foot of this screencap. I can't imagine they'd work at the wide end of an 18-135, but may at the long end

Andrea K · 05-12-2021, 06:47 AM

IMHO the most important are: disable the focus peek and do some test shots

**MossyRocks** · 05-12-2021, 09:26 AM - **1 Like**

Originally posted by damianc

I can only speak for their use on a 400mm astrograph where they are brilliant. I'd note the caveats at the foot of this screencap. I can't imagine they'd work at the wide end of an 18-135, but may at the long end

As one goes shorter you need finer slits in the mask. From using the Lonely Speck one that has very fine etchings on a clear solid filter it sort of works on the wide end of things (wide being below 100mm) but I think it may be able to be improved substantially by getting the etchings filled with a dark opaque color. To that end I wonder if I could color it with a black dry erase marker and then wipe it off the marker from the smooth clear parts and resulting in filling the recessed etchings with black ink that wouldn't be wiped away. I've use my other ones with lenses as short at 200mm and haven't had issues but then the other ones I have are specific to my 300/4 and 400/2.8. With the one for the 400/2.8 I have used it with that lens with the 1.4X-L and 2X-L converter attached as well for a 560/4 and 800/5.6 setup and it works great at those lengths as well.

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
Can a power zoom lens be manually zoomed?	macman24054	Pentax SLR Lens Discussion	5	11-28-2020 05:06 PM
K-7 JPEG Quality four stars vs. three stars	PentaxRev	Pentax DSLR Discussion	14	04-02-2016 07:49 AM
Changes aperture when manually focusing?	kadajawi	Pentax K-5 & K-5 II	10	06-27-2014 10:58 AM
best manually focusing wide zoom	seadog	Pentax SLR Lens Discussion	9	10-22-2011 07:56 PM
Manually focusing @ infinity	simonkit	Pentax DSLR Discussion	3	08-21-2007 11:41 AM

05-12-2021, 05:33 AM	#16
GUB Loyal Site Supporter Join Date: Aug 2012 Location: Wanganui Photos: Gallery \| Albums Posts: 5,762	An astronomer mentioned this technique tonight at our camera club meeting. Has anyone used the bahtinov filter.? They are available https://www.aliexpress.com/af/bahtinov-focusing.html?d=y&origin=n&SearchText...20210512042112 Attached Images

05-12-2021, 05:46 AM	#17
damianc Pentaxian Join Date: Nov 2012 Location: Highlands of Scotland Photos: Gallery \| Albums Posts: 360	I can only speak for their use on a 400mm astrograph where they are brilliant. I'd note the caveats at the foot of this screencap. I can't imagine they'd work at the wide end of an 18-135, but may at the long end

05-12-2021, 06:47 AM	#18
Andrea K Pentaxian Join Date: Mar 2009 Location: Rome, Italy Posts: 822	IMHO the most important are: disable the focus peek and do some test shots

05-12-2021, 09:26 AM - 1 Like	#19
MossyRocks Loyal Site Supporter Join Date: Nov 2017 Location: Minnesota Photos: Gallery \| Albums Posts: 2,982	Originally posted by damianc I can only speak for their use on a 400mm astrograph where they are brilliant. I'd note the caveats at the foot of this screencap. I can't imagine they'd work at the wide end of an 18-135, but may at the long end As one goes shorter you need finer slits in the mask. From using the Lonely Speck one that has very fine etchings on a clear solid filter it sort of works on the wide end of things (wide being below 100mm) but I think it may be able to be improved substantially by getting the etchings filled with a dark opaque color. To that end I wonder if I could color it with a black dry erase marker and then wipe it off the marker from the smooth clear parts and resulting in filling the recessed etchings with black ink that wouldn't be wiped away. I've use my other ones with lenses as short at 200mm and haven't had issues but then the other ones I have are specific to my 300/4 and 400/2.8. With the one for the 400/2.8 I have used it with that lens with the 1.4X-L and 2X-L converter attached as well for a 560/4 and 800/5.6 setup and it works great at those lengths as well.