Lens adapters: flange-to-flange distance

Today I received a “K&F Canon EOS-M4/3 PRO” adapter (bought from https://www.kentfaith.com/). This is a new design advertised as being of high precision. I was specially interested as this is one of the very few or maybe the only series of relatively low cost adapters with a non-reflective black interior finish. This is is important to prevent reflections that otherwise degrade image contrast or create flare and ghost images. Please see Black anodised aluminium in IR and Commlite products: how I wasted my money. Continue reading Lens adapters: flange-to-flange distance

Lens adapter with filter drawer

I here describe my experience with the DEO-TECH OWL EF/MFT lens adapter. The adapter is available mainly through astronomy web stores and seems to be currently distributed by Optolong. It is also available on special order at B&H photo video and possibly other large shops. Development of the adapter was initially  funded through Kickstart crowd funding.

DEO-TECH OWL EF/MFT adapter

Continue reading Lens adapter with filter drawer

UV-cut filters

As described in the post UVIR-cut filters both absorptive filters and interference filters are sold as UV-blocking filters. All modern photography digital cameras have internal UVIR-cut filters and most modern objectives transmit little UV-radiation. There are some exceptions, most if not all Olympus cameras are sensitive to long-wave UV-A radiation and a few modern objectives also transmit long UV-A radiation. Many filters sold as UV-filters do not differ from those sold as clear protection filters enough to matter. However, a few UV-filters do absorb in the whole UV-band and even into the visible violet band. Their effect might make a difference in high UV environments such as high elevation mountains and snow in sunny weather. On the other hand, most photographers us UV-filters to protect their objectives. For such use the most important considerations are well polished and parallel surfaces and control of reflections to prevent flare and ghosting. Only photography using film and older objectives benefits significantly from the haze-cutting effect of UV and skylight filters. Continue reading UV-cut filters

UVIR-cut filters

Filters can block radiation either by reflection or absorption. Absorptive filters are usually made of glass containing various metal ions while cheaper plastic filters tend to be coloured with organic dyes. There is a third type of absorptive filter, which are rare nowadays that consist of a coloured gelatine layer in-between two glass sheets. Most high-quality absorptive filters sold for photographic use are made of solid glass and absorptive. In the case of square filters plastic is more common than for smaller circular filters. The current perfected version of the gelatine-between glass filters is Tiffen’s “core technology”. With absorptive filters the angle at which the light impings on them affects the path length so that absorbance increases when the angle of incidence is shallow. This effect is small enough to be rarely noticeable in photographs.

Continue reading UVIR-cut filters

Godox AD200 flash for UV, VIS and IR photography

[Updated 2019-07-18] Godox sells a medium-power flash called AD200 with interchangeable heads and several accessories like light modifiers and remote wireless triggers with TTL exposure metering and high speed synchronization capabilities. This gives a lot of flexibility in its use. After a few separate purchases I now own the AD200 and the H200, H200J and H200R heads, an Xpro-O TTL Wireless Flash Trigger, and several light modifiers, all of them branded Godox. (The same flash and accessories are also available under other brand names.) Continue reading Godox AD200 flash for UV, VIS and IR photography

Digital UVA-photography with M43 equipment

How far can we go, with off-the-shelf equipment

One question which I have been pondering for some time is: do I need to have a digital camera converted to full-spectrum for UVA photography? and are there any modern objectives that are good accidental UVA-objectives?

This is not a question of cost alone. Although a converted camera can be used for VIS photography, obtaining good colour reproduction requires effort. A suitable filter is used on the objective to replace the one removed from the image sensor unit during conversion. As it is not possible to find a perfect match to the filter removed, one or more colour profiles of the camera need to be created and applied instead of the one used automatically by the camera and/or raw file converters. So, in many cases, for best results one would need to carry two different cameras to any field trip. In addition a conversion voids the camera manufacturer’s warranty and even access to official service facilities. Continue reading Digital UVA-photography with M43 equipment

Oversized lens hoods and windows

I read during the 1970’s, most likely in a photography magazine, about the use of collapsible rubber lens hoods to take photographs through windows. They do work, specially if one manages to find a stiff enough one that will not collapse instantly at the first bump in the road or in the flight. Hama branded rubber lens hoods did work well for this purpose 45 years ago and those currently available from Hama also do work well. The problem is that given their size one has little room for deviations from pointing straight into the window as vignetting quickly becomes a problem. Neither can one use them with wide angle lenses. Continue reading Oversized lens hoods and windows

Most neutral density filters are not neutral

[Updated 2019-07-17] A neutral density (ND) filter is a “grey” filter, a filter that transmits equal fractions of the incident radiation at all wavelengths. A perfectly neutral filter over a broad range of wavelengths is an idealized concept, and one very difficult to implement in practice. There are different approaches to making filters approximating colour neutrality. We here compare the spectral transmittance of of ND filters of three different types available for use on camera lenses and explain why the use of some of them can introduce strong colour casts in the photographs we take with them.

Continue reading Most neutral density filters are not neutral

How small a spectrometer can be made?

[I will update this post after testing the sensor]

In a recent post I described a miniature two-channel UV-A sensor with digital interface. Here I will describe a miniature and low cost spectrometer, type AS7265X from ams. It does not used a grating as monochromator, but instead each of the 18 channels has a different interference filter deposited directly on the silicon chip. The FWHM is 20 nm, and the wavelength range from 410 nm to 940 nm. The spectrometer consists in three separate sensor units working together. The interface is digital, and temperature compensation and analogue to digital conversion takes place in the sensor modules. In spite of the number of channels communication between the spectrometer and a micro-processor requires only two wires. The spectrometer supports two different communication protocols, the specialized I2C and a generic serial communication (UART).

Macro-photographs of both sides of an early prototype of a breakout board are shown below. The size of the board is 18 mm √ó 19 mm. (Photographs were taken as described for the UV-A sensor.)

I bought this board from a seller at Tindie for USD 50. The seller is now selling a differently shaped board, with the three modules in a triangle, and so closer to each other.

More on taking photographs through windows

The “Ultimate Lens Hood” seems like a good tool. It is still to be seen if it is stiff enough and/or a bit sticky so as to easily stay in place on the glass surface. It has the potential for being very useful but how easy it will be to handle with different lenses is still to be seen.

I just made my pledge for one ULH at Kickstarter. If you want to get your own, be aware that the campaign is about to end.

An oversized conical bellows of black silicone: the “Ultimate Lens Hood” (ULH).

See my earlier post to learn how I have been managing until now with normal collapsible lens hoods made of rubber. I recently uploaded a gallery of photos from an ongoing project where I am taking photographs through train windows.