UVIR-CUT filters from Alibaba... or Optolong L-Pro?

[bojan]

I found couple of ads on Alibaba for UVIR-CUT filters at very attractive prices (10 - 50 US$ .... bargain compared to Astronomik or Baader Planetarium prices), performance on ads looks good, but the overall presentation on Alibaba website somehow doesn't fill me with confidence, I have a feeling that both sellers and buyers do not know exactly what is going on and what will be received at the end of the day... especially after (bad?) experience with seller on ebay where last year I bought Rocolax filter with advertised transmission BW to be 400-700nm, but actually it turned out to be ~ 400-640nm - good for general photography, but not suitable for AP.
(I am sure somebody in the supply chain made a mistake or did not check properly)

Does anybody have some advice or comments?

[ZeroID]

Been dealing with Alibaba for a while, my electric bike kits come through there and I've picked up a few other bits no problems. Always quite quick on delivery, sometimes for free. Always received what I've ordered although they haven't been as critical as filter specifications.

[glend]

I have had good and bad experiences with Alibaba sellers, and some mainland Chinese sellers are very slow to deliver. Be aware of the February shutdown of business in China due to their new year holiday period, which affects some businesses for two weeks.

I used to buy Canon DSLR parts on a regular basis and woukd say 70% took about six weeks min to receive.

For something like an astro filter, i would stick to the respected brands with a history. There is a supplier in Hong Kong, Cyclops Optics, which i have purchased from - bought a cheap set of Optolong RBG filters (low cost Chinese brand). They are ok -just. I would not buy their narrowband filters however. You could look at ZWOs filters but i believe they are identical and from the same source supplier as the Optolongs. Both ZWO and Cyclops are Alibaba sellers. The Baaders and Astronomiks etc give you very precise specs, excellent multicoating, etc. I use Baaders for narrowband, purchased from Teleskop-Express, no regrets.

[bojan]

Hi Glen,
Thank you....
Optolong L-Pro (https://www.cyclopsoptics.com/filters/optolong-l-pro-filter/) filter looks OK.... a bit expensive but probably worth it.
UHC (https://www.cyclopsoptics.com/filters/optolong-uhc/)is cheaper...
I will consider.....

[bojan]

Just purchased unmounted 36mm L-Pro filter from Cyclops... It seems to be the better option than UVIR-CUT filter because it is also LP filter.
According to Cyclops, it is the same glass used for Clip-On variety..
So I decided I will 3D print the holder.
But... before starting my own design, I had a look at Thingiverse.. and found this (http://www.thingiverse.com/thing:1184617) design.
It is for 1.25" filters, so I will have to modify the STL file, as the central hole needs to accommodate 36mm x 2mm glass (this can be done by loading stl file into 123D (freeware from AutoDesk) and subtract the appropriate cut out.
This "fiddling" will save me $67... not insignificant amount.

For more general applications in the future (for other cameras and telescopes), this (or similar) design (http://www.thingiverse.com/thing:91390) will be useful as the principle.

I am still looking for low-cost solution for UVIR_CUT filter on Alibaba... so far the lowest price is US$50 for 50x50mm sample.

EDIT
Because the design from Thingiverse is for 1.25" filter, 36mm glass will not fit into frame... So I will have to design my own, with lower profile springs.
I will post the design here when tested.

[glend]

Bojan, ZWO has a 2" Round IR Cut filter on their website for $49 USD.

https://astronomy-imaging-camera.com/products/filterfilter-wheel/zwo-2%e2%80%b3-ir-cut-filter/

There are a number of cheaper ones in smller sizes. You might be able to use one of the UV-IR Cut sensor cover windows and print a carrier for that. Sizes vary from 1.25 up. Don't pick an AR window as they do not block.

[bojan]

Hi Glen,
Thank you for the tip.
It seems all those filters are coming from the same source, as transmission plots are (sometimes) identical (as if those guys just copy-paste the data one from another).

Anyway, I will consider this filter for next month, right now my "allowance" is used 120%.

[bojan]

I was searching for converter of *.stl file into *.dxf and found this online utility:
http://www.cadforum.cz/catalog_en/stl2dwg.asp

It worked OK, and resulting file could be opened in LibreCAD (which is 2D). I have yet to try this with some 3D cad.

Also, there are other utilities that may help editing stl files:
https://all3dp.com/free-stl-editor-open-edit-stl-file/

[bojan]

3D print looks good.
Now waiting for filter to arrive.

[bojan]

While waiting for L-Pro filter to arrive, I contacted seller on Ebay from whom I purchased Rocolax UVIR-cut filter last year (it was $70!)
They promised to send me the new one (hopefully the wider one).
To strengthen my case, I put together my Hartridge spectrograph, calibrated the wavelength with energy saving bulb and processed images taken with $5 webcam in BASS software..

Instead of cutting off wavelengths above 670nm as per ad, the cutoff starts at 645nm.
I am hoping for the best outcome...

Also with the same setup I will be able to check L-Pro filter as well.

[sil]

it seems wavelengths and China dont work out so well. I spent ages trying to find UV torches that actually were UV and not just purple torches, they just don't match the wavelengths listed and yes specs are just copy/pasted to fill in product descriptions. I've got a nikon clip-in filter from cyclops on its way, they've been great to deal with and I've got confidence in their listed product specs.

fyi, TinkerCAD is also a good online free 3D program for modifying 3d files for printing. It does a better job at some things than LightWave3D (which I've been using 15-20yrs) and I can work between both easily, if only my aldi 3d printer was so easy!

[bojan]

What is curious here is that Gary Honis is (re)selling 2" Rocolax UV-IR Cut filter and he told me it is quite OK for H-alpha.... So there must be a couple of varieties, all manufactured by uvircut.com (they or their office seem to be in Taiwan, and I tried to contact them directly but there was no response..)

[bojan]

L-Pro filter is here...
Test says it is probably OK, ~3x more H-alpa compared to Rocolax (y-axis calibration/linearity (gama) is still questionable).
Due to small sensor of this $5 webcam, only red part of the spectrum was captured.

Hopefully, it will be clear tonight....

[bojan]

I changed a concept slightly....
Adapter is still clip-on but to M42-EOS adapter.
The position of the filter relative to sensor is the same as conventional clip-mount, but the filter is attached to the lens/scope.
This way I have more flexibility in use of modified or unmodified or any camera in combination with any lens/telescope I have (all of them have M42-EOS adapter).
This adapter is easier to print with lower tolerances (0.1mm layer thickness, 85% infill, printing took 16 minutes) and the fit inside camera is better, it is tight but the elasticity of the material is sufficient to ensure self alignment.
Now I need a clear, light-polluted sky to test the whole thing, it seems Melbourne will be blessed with all that tomorrow.
Please note, the adapter ring is not solid, I made a cut (visible on the image at the away side of the adapter) so it could be widened to accept the filter.

[bojan]

Results of test from last night are attached.
While the contribution of the filter to LP extinction was somewhat disappointing (~50%... but still significant), the focus is drastically better.
However, some stars on the image are still bloated (halo is greyish), I think this may be due to presence of IR.

BTW, I returned Rocolax UVIR-cut filter to seller, they promised to send me back the correct one (hopefully they will perform some tests to ensure that... ).

[speedyjim]

Ever tried a Hoya 49mm uv-ir cut filter? For a 2" filter they work out cheap and have full cut off at 700nm and appears it only starts to cut at 680nm. They are way cheaper than baader etc. You can remove from filter via spring circlip and use unmounted... Thoughts?

http://www.hoyafilter.com/hoya/products/generalfilters/uvircut/

[bojan]

Hoya was on my list, but it was quite expensive.. so I thought this L-Pro will do the job + LP... IR cut off is the same as Hoya, as per my own measurement.
That Rocolax was supposed to be the same as Hoya (for 1/3 price) , but it seems I received the wrong one.
The new one is on the way, we shall see what happens.

[JA]

Hi Bojan,

Nice comparison of the with and without LP filter.

I did something similar with a didymium filter on Orion and have been meaning to post the image as part of my quest to reduce the effect of LP. Your thread has reminded me to do so, so I will soon. If you'd also like to try these filters in your fight against LP, since you're in Melb, let me know. I may have one in a size that you could borrow.

Best
JA

[speedyjim]

I managed to get one off Amazon for $75 delivered. Most others were selling for $100 plus delivery

[bojan]

Thank you for the offer, I will PM you when I am ready :thumbsup:

As for comparison....
the attached images below were taken with the same lens, left one is with unmodified 60D (last year), right one is with 450D FSM + L_pro (last night).

Some stars (with L-Pro) have halo, some others (of same or even higher magnitude) don't.
There are no halos on corresponding star images taken with unmodified 60D.
The difference is most likely in spectral type and excess of IR (most likely) or UV (I don't know yet what L-Pro filter does compared to Canon filter in 60D)
So, it seems more filtering will be needed to fix this (IR? I will know when replacement UVIR-cut from Rocolax arrives).

[JA]

OK sure.



If you use a normal camera lens you could possibly rule out the 450D haloes as being caused by excessive L_pro UV bandwidth, by also stacking a lens mounted UV filter on to your lens, which should remove most of the UV and then check again for haloes against another non-UV filtered image, preferably taken at same time with same exposure.

In a round about way you could do something similar for the Infra Red end of the spectrum as well if you have some sort of photographic IR filter (like an R72 or the like). Except that this time you'd be looking to possibly find the halo in the Infra Red image. If you find the halo in the IR image then bingo.

Another possibility for the haloes, relates to the 450D's Full Spectrum Mod - When the UV/IR filter was removed was it replaced with clear glass of some type or left empty? My thoughts would be that if left empty or if the replacement glass is not of the right refractive index, it could cause a tiny deviation in the intended focus of infra red (if enough IR is coming through to be apparent) , in that it may not focus soon enough, which one would probably see as a sort of chromatic aberration (except not Red, Green, Blue, Magenta..., as IR is not represented by the sensor in that way, but mostly as deep deep brown/red or grey and would represent as a halo. Or maybe there's just too much Infra red bandwidth picked up by the sensor, which the lens is not able to focus closely enough to the visible light focus, either way I could certainly see it would represent as a halo of some sort (and a slightly defocused image) - see below... (coming soon .... :D)

EDIT: .... Now added as diagram below (that was fun !!!)

[bojan]

My modification was simple - no glass plate instead of removed filter.
Yes, I think you are right, it is IR.. I looked at couple of stars with halo and all of them have colour index >1.5, which means they are really red.
However, I am not sure the observed effect is because of removal of the glass, because uvir-cut filter is 2mm thick.. it is at the different location but still...
Most likely it is because this lens is Canon FD 400mm f/2.8L, from '80-ies last century, not corrected for IR.
And spurious far-IR bandpass of the uvir-cut filter (I will have a look with spectrograph tonight if it exists or not) allows too much IR.
BTW, all bright (saturated) stars have the ~same diameter, which is also indicative of something un-expected and counter-intuitive going on here.

[bojan]

There is also a tiny possibility of internal reflections inside L-Pro filter....

All will be clear once I receive the replacement for UVIR-Cut filter...

[bojan]

Rocolax UVIR-cut filter replacement arrived yesterday, I tested it with spectrograph and it turned out it is almost exacly the same as previous one...
So, most likely this problem I have is not about manufacturing quality but rather it is because distributors do not really know what they are selling...
After some more googling, it seems that this filter (with cutoff at 650nm) is pretty standard...
It seems there are two other cutoff wavelengths set at 700nm and then 800nm...

[bojan]

The new uvir-cut filter (680nm, from LenOpTec) arrived today.. it looks very good, H-alpha is passed almost un-affected (green plot, compared to Rocolax which is 650nm)
Halos disappeared with this filter... so the problem was caused by IR (between 670-700nm and possibly beyond 1100nm).

[bojan]

I did another filter test last night with Canon 450D (FSM) and Canon FD 400mm f2.8 (@f4).
The combination performs very good IMO, with focussing with Bahtinov mask (the star to focus on should be G~F type.. I also tried with Betelgeuse but the Bahtinov pattern was somewhat ambiguous and resulting focus was a tad off... obviously the lens issue).

The uvir-cut filter comes from LenOpTec (Beijing, the contact person was Oswyn Tu, info@lenoptec.com), the service was exceptionally good (they posted the item 2 days after receiving payment via PayPal).
Two filters plates 1.1mm thick (I asked them to cut it in round shape, 45mm dia, so I could mount the filter into Canon filter holder to replace "standard" neutral glass) cost me US$50.00 +US$25 for postage via TNT.
I imagine the other shapes and sizes are not the problem for them.

Compared to Hoya, Baader Planetarium and Astronomik prices for such filters, LenOpTec filters are absolute bargain... and the published data very closely match my own measurements.

[JA]

Good Stuff - Looks like you're in business :thumbsup:

Best
JA

[bojan]

Yep...
This is nothing much, but illustrates the result.
Second attachment is 100% size crop from 16x120sec stack.