Brand new T490B - extremely yellow?

[Shivs]

Hi Guys,

new scope arrived, such an upgrade to my crappy omax. I am a bit concerned with how yellow it appears. I have tried using the blue filter and it appears closer to normal but still not quite right. I knew halogen bulbs were supposed to be yellow but this is quite pronounced

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[Greg Howald]

You may well need to adjust the white balance on your camera. It can get rid of most of it. The camera really enhances the yellow color out of the box. You will find halogen to appear yellow but halogen light is actually very red if you look at its spectrum. If you had gotten the led scope you would probably be dealing with blue light. There's no real cure for either but you'll do better with a blue filter with light hue and you'll probably have to make that. Glass blue filters that come with these scopes are usually too dark. A lighter color will help.
The 490 is a really good scope. It's a popular best seller and is very versatile in what you can do with it.
I hope you are able to enjoy your experience.
Greg

[Shivs]

thanks greg, I just adjusted the color temp in the software and it looks great.... looking through the lenses is still super yellow but im most concerned with how photo and video will turn out....

This thing is like night and day compared to the other scope I had.. now just waiting for the new cam, so excited!

[Red_Green]

I don't know what's going on there but as an owner of the T490B, I can confirm mine has never looked this yellow. I mean the halogen bulb gives off a bit of orange or whatever but just as much as any other scope I ever used. Almost looks like the yellow filter disk is in.

[hans]

Per your earlier post, if the goal is to minimize exposure time to keep video frame rate high you are probably better off not using the blue filter and correcting in software. The blue filter blocks quite a bit of light overall and requires significantly longer exposure time. In theory using the blue filter should reduce chroma noise since the color channels are being exposed more equally but I noticed little difference with a Reichert Microstar IV (also 20W halogen with switchable blue filter) and Nikon D5100.

[hans]

Yeah there is also the question, what is actually in there? Is it actually a high-temperature (like 3200K+) halogen?

[Greg Howald]

Different bulbs seem to have different affects. I have one 20 watt halogen that is very yellow and another that is not. The one that is better is branded as Phillips and the one so yellow is no brand generic. I wonder why but it may have to do with the gasses in the bulb.
Greg

[Shivs]

the bulb is a 20w 6v default that was in the scope. There is a 2nd replacement bulb but not sure if I want to try changing it quite yet.

[hans]

I have not bought any generic bulbs new but experience with ones that came in microscopes I bought is similar to Greg's -- suspicious the cheap generic ones "cheat" by just using a larger, lower-temperature (so yellower and less efficient) filament that relies less on the the halogen cycle working correctly. Could try something like OSRAM 64250 HLX which are 460 lm at 3350K color temperature.

[Shivs]

thanks, grabbed these
https://www.amazon.ca/dp/B015OTJTUS?psc ... yp_imgToDp

might take 2-3 weeks to get here so Ill live with these ones.

[Shivs]

FYI, I swapped the bulb with the spare in the box.. exact same. Not sure what crappy bulbs they are including. Hopefully the ones I ordered come soon.

[hans]

3350K is still noticeably yellow to the eye but hopefully you see an improvement. What white balance setting were you using when you got the really yellow-looking photo? Does the camera software have a white balance mode where you manually set the color temperature?

[Shivs]

3350K is still noticeably yellow to the eye but hopefully you see an improvement. What white balance setting were you using when you got the really yellow-looking photo? Does the camera software have a white balance mode where you manually set the color temperature?

heres a comparison with default and 4600

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[hans]

Hmm, no way the illumination is actually 4600K with no color filters in the path, and when I set 4600K in RawTherapee I get the result attached below. Using the color picker gives values in the 3000-3100K range, much more believable. Camera software implementation of color temperature seems a bit suspect?

[Shivs]

Camera software implementation of color temperature seems a bit suspect?

No clue, I'm using the omax software, I have a new amscope cam on the way but I think it uses the exact same software.

[MichaelG.]

I can’t help regarding the actual ‘scope, or its lamp ... but let’s just consider some basic physics:

A tungsten filament is a good approximation to the hypothetical ‘Black Body’ and its radiation spectrum is very predictable.

The spectral density shifts towards the Red at lower filament temperatures, and towards the Blue at higher filament temperatures ... This is, of course, the basis of Colour Temperature [with or without the u]

The Quartz Halogen cycle serves to reduce blackening of [and filtering by] the bulb itself ... and, to work properly, the lamp needs to run hot ... in other respects it is just another ‘filament lamp’

The only thing likely to substantially vary the colour of your tungsten light is the current passing through it, and hence the filament temperature. ... There are no hidden secrets to this basic phenomenon !

Start here: https://sciencedemonstrations.fas.harva ... ation-lamp
Then look at Fig 6.2.2 on this page: https://phys.libretexts.org/Bookshelves ... _Radiation
... and this excellent summary: https://www.giangrandi.ch/optics/blackb ... body.shtml

MichaelG.

[apochronaut]

You have to run halogen bulbs at no less than 85% voltage , better 90% , otherwise they will burn out prematurely and burn with a yellow colour. That's why professional microscopes have multiple filtering built in. You use filters to adjust intensity and colour balance, the field diaahragm to adjust contrast. The condenser can be used to adjust for N.A. somewhat and intensity somewhat but with higher N.A. objectives it needs to not be set so as to not reduce resolution while you are trying to reduce intensity.
In short N.D. filtering and tweak the voltage for intensity but keep the voltage up there.

[Shivs]

Thanks for all the info, I also found these bulbs:
https://www.bulbs.com/product/ESB-FHE

[Red_Green]

thanks, grabbed these
https://www.amazon.ca/dp/B015OTJTUS?psc ... yp_imgToDp

might take 2-3 weeks to get here so Ill live with these ones.

I'm thinking about ordering these bulbs there. Are they any good? Have you tried them?

[microscopeboi]

Like others have said im almost positive its due to the bulb. Try to get a white light LED

[GeekyWife]

I've never seen anything anywhere near that yellow iny stock T590B using the supplied 20 watt halogen bulb.

When I compare the color of the light with the color of my LED SE306 stereo microscope light, of course the halogen looks more yellowish and the LED more bluish. But without that comparison, the halogen light just looks white, or slightly off-white.

[MichaelG.]

I have to say: I think this is either a faulty camera, or faulty software settings.

Unless the bulb is being severely under-run, it should never produce that colour of light !

MichaelG.