Review - ultra compact AstrHori AH-M1 light meter for camera shoe mount

 In this article I'm going to review quite interesting device - ultra compact AstrHori AH-M1 camera light meter . I just received this copy today directly shipped from Pergear (thank you!), so will be posting their non-affiliated links as a gratitude. Though as always you should expect very transparent and unbiased review, where I share personal impressions from experienced quality engineer angle of view.

Light meter unboxing

Box arrived securely packed, it's covered with various branding names, perhaps due to cross-countries marketing strategy. One side shows AstrHori logo, other side has Rock Star logo, which both belong to Bozhendao Technilogy Co., ltd .

Surprisingly the light meter picture on the box top does not match the released model, perhaps it is picture of earlier prototype, and screen information there is similar to DOOMO light meter digital screen. I think it's just typical print flow rush mistake where designer forgot to update picture to production model and it was too late to correct.

Box is sealed by stickers with user friendly leaves and open marks, I like that.

First look into the box. There is high-density foam nicely protecting content during transportation, and is separating AstrHori AH-M1 device from USB charging cord. Hex wrench is puncturing the foam to keep its place - that's interesting, though I appreciate that wrench is included, perhaps for remounting.

I've checked the manual first and it is very well written with lots of translation effort done. There is minimal number of mistakes of typos comparing to other manuals and everything is very well logically explained. I think if you never used light meter - included instructions will be also quite educational.

The size of AstrHori AH-M1 light meter surprised me! It is very tiny, though the weight is noticeable in hand and making to feel it as quite solid piece of good engineering effort. I even spent extra time to find AA battery for easy size comparison. Yeah, in a modern world people still use AA batteries.

There is number of mount holes on the rear side and USB-C connector. Some of my cameras also have USB-C, so it's nice to use same charger when needed. Manual tells that full recharge should take about 40min, which much less than typical charging of much larger capacity camera battery.

I checked first that light meter is working by pressing the rear button. Then mounted it on Leica M10P to check the shoe fit. On this camera it is slightly loose, so I'll probably add a thin layer of vinyl tape to mount bottom later (though it fits more firm on Fujifilm X cameras when I checked later).

I wish there were a black version of AstrHori AH-M1 light meter - that would look more organic on this camera. Though it's just the cosmetic look which can be addressed by painting, what I'm more interested now is functionality. I never used separate light meters before so it will be quite interesting experience.

I've set the aperture value, which is double-pressing rear button to choose aperture mode, then rotating top dial to desired F2.8 . Then I realized the guide is a bit confusing with that double-press then second slower press in operation steps. It took a minute to realize that guide means single press quickly followed by longer 1sec press and hold. 

While reading guide real time metering captured attention. AstrHori meter is metering by default only when you press the button - then single measurement of light is processed. To enter continuous metering mode called "real time" you simply press and hold button until circled arrow symbol appears in bottom right corner.

When real time mode is enabled, it's also possible to single press button to lock measurement for 10 seconds.

Then I decided to change the shutter speed to what light meter recommending and realized that I can't see the dial. Light meter is covering half of it.

So I'm following manual and shifting mount to the most right position using included hex key.

Then mounting it back to camera. Yeah - that's much better, now I can nicely see whole shutter dial.

I'm changing to ISO100 on camera and in AstrHori AH-M1 light meter. Now it's recommending 1/250 shutter speed.

One of the benefits of this light meter - it is showing light intensity in EV range, e.g. EV11 in this time telling that it is possible to capture up to 11 steps of exposure range. In much darker conditions that number will be much lower, even though you can take correctly exposed and illuminated picture, but level of details in highlights and shadow will be significantly lower as well as overall picture tones details.

Another benefit - is to have a small upper screen showing you exposure measurement right where you can also see lens aperture and camera ISO and shutter dial value. It's quite nice to have when also shooting using hyper focal focus distance where you don't bother with lens focusing and approximately know area of framing for shooting from hip position.

One thing to keep in mind regarding the camera you are using. E.g. this Leica M10P is showing exposure based on Central Metering while looking through viewfinder. AstrHori AH-M1 light meter is performing light scan in approximately 30 degrees angle according to manual, which is making it closer to Average Metering of the area covered by that 30 degrees view angle.

I've compared camera metering details to what AstrHori is showing and realized that difference is quite consistent across randomly changed ISO and aperture values. In most cases this external light meter is showing around -0.6EV darker exposure. That can be easily aligned by entering EV compensation with rapid press followed by 3sec press and hold to set +0.6EV.

I've also tested light meter on Fujifilm X-Pro3 camera with attached Voigtlander 23mm F1.2 lens. I've set camera metering to Average too, and exposure measurement difference was also averagely -0.6EV, but with that EV compensation measurements remained consistent with camera across different aperture values, ISO and shutter speed.

I'll need to spend more time outdoor during next few days with this light meter to better evaluate it's practical precision. And will update article with more details on that.

Light meter disassembly

Small size, noticeable weight made me extra curious to see how it is built inside.

First step is to unscrew two bolts located on bottom corners of light meter, and included hex wrench fits for that bolt heads.

Once metal bottom panel is accurately pulled out you can see energy cell of li-ion battery. Battery contacts are well isolated, but definitely it is not a water resistant design, so make sure you never expose it to rain during use.

One thing alerted me here - you may notice circle marks on the battery protective coating layer. They appeared due to pressure of bottom plate with slightly protruding edges of mount sockets. The inner side of that plate is not flattened after screw sockets drilling and that may cause a problem.

WARNING: if for any reason you decide to remove shoe mount from AstrHori light meter and screw in that three black bolts back just to not miss them - do NOT do that. Because without mount piece bolts can be screwed in much deeper - which will result in puncturing and damaging li-ion battery. And we all know that this type of battery does not like to be damaged.

I'm taking out the battery to check the electronics. It is made of dark material usually found in more premium electronics. There is large text "BZD_LightMeter_v1.0" and wide screen ribbon cable connector to the left.

Only single bolt is holding the board, I'm unscrewing it and accurately pulling out the board. Opposite side has OLED screen and rotational controller. Note that screen is not protected with any sort of glass or thick plastic, so it should be handled with care. Do not store this AstrHori AH-M1 light meter in a bag with sharp objects.

The thin strip of transparent plastic in tweezers is from the area behind the light meter input hole. Looks like it's there to protect internals from incoming dust.

I'm pressing the button to check how is it operating without casing. With that huge amount of light it is recommending shutter speed 1/6400 which is not surprising.

Light meter casing is made from metal alloy that looks quite durable and is covered with thick layer of another protective layer that may be a paint or electrically applied coating material.  I can see spring loaded ball when looking in between top dial and upper light meter surface. The top dial can not be removed. Looks like the inner rotation controller shaft is hard pressed into top dial central socket.

Here's the closer look at the light metering sensor.

I decided to add thin vinyl film screen layer to sensor edges facing internals to block any stray light that may come in. I don't think that makes any difference though comparing to the light amount collected by sensor directly.

At this point I'm assembling AstrHori AH-M1 back, putting extra care to the li-ion battery location and making sure it is not deforming under bottom plate. I think tomorrow I'll grind inner surface of bottom plate to make it more safe for the battery.

I had four battery bars on meter so decided to charge it for 10 minutes and number of bars increased to 5 after that. I didn't notice any significant warming up of battery area even though the casing should nicely conduct temperature.

Brief Conclusions

There are up to a dozen of different compact light meters on the modern market and I'm glad to see how different manufacturers are evolving and polishing the technology while trying to keep the budget affordable. For sure it can't compete with robust and time proven design of older classic compact light meters, it's simply due to more time is needed for each product to evolve. From the other side these modern light meters and AstrHori AH-M1 as well are offering new interesting and useful practical features while attempting to keep the size and styling properly fit to use with film and digital cameras. I think this reviewed model has its own unique benefits, and hope that some found flaws can be addressed in next production line or next models without significantly affecting their price.

It's also great to see all metal framing and mount customization as well as more transparent user guide and intuitive user friendly interface. One thing I'd like to see is better protection of built in battery and screen surface. Control wise it's nice tiny device and a joy to use.

I'll need more time for intense practical use of this light meter to share more feedback. I'll find more opportunities over the weekend for a photo walk and taking pictures relying only on this tiny light meter for exposures setup. That should be fun! : )